1LoudLS

well since its not a base model and it has the full speaker package, an amp wouldn't be needed (unless you are shooting for an excellent sounding system)
the two biggest things that are going to affect the sound quality are going to be changing the speakers out for a quality set to get better and clearer mids and highs, and then a small subwoofer to add in the low bass that smaller speakers just cant reproduce on their own. (good news is that the new spark finally got their stuff together and are building them with normal sized speakers instead of the tiny speakers in the older models)
depending on what your looking for, a great set of speakers would probably cost you between $200 and $300 for both pair (possible less depending on where you're shopping) and for instance, my favorite go to models of speakers to recommend are pioneer D series (models starting with TS-D) and lately have been finding them four under $70 s pair (components with separate tweeters will cost a bit more) and the retail on them when places like best buy carried them was around $200 a pair!
as far as the sizing goes, haven't seen one yet and my fit guide information hasn't been updated yet. I'm really hoping they went with the most common size speaker in the world and the same size that is in 90% of other chevy's which would be 6.5", since they are large enough to actually provide some decent bass.

I'm sorry, but anybody that thinks they are getting any better performance from higher octane fuel is just arguing against science. you are no different than people that still think the earth is flat or that we haven't been to space. they oblivious work in a profession that is far different from that of engineers that design engines, engineers that test those engines, technitions that built or work with high performance engine building or that work in engine tuning.  those people actually work in science, they are actually doing the math and need to know what the difference in octane actually is and what it means during the combustion cycle.   
 
in a modern fuel injected automobile, for the most part, the compression ratio, air temps, and how aggressive the engines calibration or "tune" is, are what dictate what octane fuel the car needs to be fed. none of that is really that high in the case of the spark, if the compression ratio was high enough, fuel with lesser octane would ignite too early causing pre detonation which will eventually(or very quickly depending on the severity) destroy your motor probably by throwing a rod right through the block.
 
if the air intake tempature was hot enough like it was being compressed by a turbo, that added with too much compression would cause the air/fuel to ignite to early causing............  
but with ambient air not being compressed before being fed to the engine means that wont be a problem causing you to need a high octane fuel.
 
in regards to engine tuning, if it was aggressive enough be having a lot of spark advance, then you would need a high octane to keep the air/fuel mix from igniting too early causing............  
but luckily the GM engineers though of that and when the knock sensor starts to detect pre detonation, it retards the timing enough to keep that from happening and preventing the motor from blowing itself apart. they also know that the spark is not a Z06 and build the engine for efficiently not full on performance and therefor tune it to walk a balance of longevity and efficiency. the stock tune is very mild and as long as your your meeting the minimum requirements, the PCM wont need to pull any timing to keep it safe, but it also is not pushing the edge and after the minimum is met, it wont push harder than its programmed to do. now if the spark had an aftermarket tune, then the tuner would likely push the timing up a few degrees making use (and requiring) higher octane. but without that, there is truly no benefit to a high octane fuel, doesn't matter if its 91, 92, Corn E85(which is really equivalent to over 100) or VP racing 114, all that extra octane is not making your bang any more powerful in your low compression engines.
 
long story short, you want the precisely controlled spark from the spark plug, not the inconsistent heat from the compression cycle to ignite the air/fuel mix. and if that precisely controlled spark is not programmed to take advantage of the benefit of higher octane fuel, then there is no more power to be made, their is no more mileage to be made, there is no measurable difference to be found.  your engine will only suck so much air in on its own, that air will only have so much oxygen contained in it, that oxygen can only allow a very specific amount of fuel to be burned with it. octane changes none of that
 
#SuckSqueezeBangBlow
#MathAlwaysWins
#BecauseRaceCar
 

87 octane has quicker combustion at lower temp and the higher octanes combust at a higher temp and burn more slowly to prevent 'pre-combustion' resulting in engine knock. Higher octane does not in any way give better performance in cars that can run the regular octane...that is a long standing myth ie: higher number + higher price = better performance quality etc.
Bottom line: low octane burns fast and ignites at a lower temp, high octane burns slow and ignites at a higher temp. simply designed for high compression engines such as found in some performance domestic cars with high compression ratios such as 12/1 etc.

next to no one makes 8 ohm speakers (for cars)
98% of aftermarket speakers are 4 ohm with a few being 2 ohm.
4 ohm speakers wont have any problems, if the factory radio couldn't handle it, all of these threads about replacing speakers with be loaded with people talking about how their radio blew up.
not to mention as in installers, I would probably be out of business if all the speakers I put in burned up factory radios every time I did it as there are a lot of cars with 8 ohm factory speakers.

I wouldn't at all be surprised if there were differences between the radios in different models, if the radio doesn't even have the option to fade in it, then it is very likely that it does not have the internal requirements to drive any more speakers... base models are all about getting the car fro as cheap as possible, and if Chevy can save even just a few dollars by being able to put a cheaper amplifier inside the radio, they are surely going to do it as when your are talking about shipping as many cars (often world wide) as a company as large as GM is, a couple of dollars here and a couple of dollars there can really add up quickly.
I agree Gearhead, if there were no speakers in the rear door from the factory, I probably would not go through the trouble of adding any unless I was trying to build a really great audio system, but if that was the case, I would probably be starting with a different car.
the problem I would have with them sounding "OK" is that I spend a lot of time in my car and since enjoying good music can make hours in the car fly by, just OK would never cut it for me. it has to sound great. and often since a lot of OEM system are pretty lacking in the sound quality department especially for how much even the upgraded systems cost, I would just rather start with a more basic system since I know I will just be pulling it out anyways.
your money would be best spent on really great speakers for the front of the car and (in my opinion) a subwoofer... adding rear door speakers would only be beneficial if you always had passengers riding back there

the issue here is that since the radio only has outputs for two speakers (two channel internal amp), there really isn't a good way to wire in and add just a pair of speakers properly.
you could wire them in series with the front speakers, but then the increase in resistance will drop the volume down so much that there really wouldn't be gaining anything in adding them (unless doing it solely for passengers in the rear. but if you wired them in parallel with the front speakers the drop in resistance would cause the current to be way too high and (with the vast majority of OEM radios) would likely burn up the internal amp before blowing the fuse. also if you somehow got a short in the wiring, the fuse may blow, or again you may just burn up the amp.
with that particular radio, the only proper way to add rear speakers would be for you to also add a small amp to drive those new speakers and there is still plenty of ways to do it wrong and damage something in the car and get your warranty voided.
its not hard to do at all, but if done poorly or incorrectly, there are definitely plenty of ways to cause a lot of damage. and with GM spending the time and money they do designing and testing all the car systems, you really cant expect GM to take any other stance on the situation. the last thing any manufacturer really wants you to do is buy anything aftermarket, they would much rather you spend more money and get their overpriced OEM options.

you will skip the spark as an option because the most basic model offered does not have rear speakers, even though you are also contemplating a slightly larger fully loaded car? I mean I get that if you want something different for your next car is cool, but seems odd that its basic offering being too basic would be something worth noting.

you will skip the spark as an option because the most basic model offered does not have rear speakers, even though you are also contemplating a slightly larger fully loaded car? I mean I get that if you want something different for your next car is cool, but seems odd that its basic offering being too basic would be something worth noting.

from past experience with other cars (GM and otherwise) that have a very basic sound system is that the rear door most likely have the wiring in place, but just does not have any speakers in the rear doors.
also, if you were thinking of just adding new speakers, it probably will not be as easy as that... chance are, since you radio does not have a fader control to fade the sound from front to back, that radio is not likely to have an amplifier for those two extra channels, you will probably have to add an amp to drive any extra speakers you want to add, or replace your radio with one that does have a full 4ch amp inside (aftermarket or possibly OEM)
unfortunately, as mentioned, that car is so brand new so it may take a little wile for them to get out and other people can tell you, probably the easiest bet would be to either pull a door panel off and see if there is a harness in there, or possible pull the radio out and see if it has pins in the right spots in the harness.

never seen electrical tape thats black on the outside and white on the inside... did you just use duct tape?

you would be better off buying this kit at a minimum
http://www.amazon.com/Metra-99-3309B-LC-Single-Installation-2013-Up/dp/B00DLEY9VI
as it comes with the data module to integrate with the vehicles CAN system.
but that is the most basic data module, 1st it wont work with onstar if you have in (and plan on retaining it) and 2nd a radio that expensive (double din kenwood nav) it would need a few extra wires ran through out the car to maximize all its features.
this would be a better choice
http://www.amazon.com/gp/product/B00DUI5J6O/ref=pd_lpo_sbs_dp_ss_1?pf_rd_p=1944687622&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B00DLEY9VI&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=11QB9DDZZ34WQFFJ8YVG
as this data module is more advanced and gets more information from the data bus system such as reverse wire (radio needs for back up camera) and parking brake (radio needs to unlock menu features)(not getting into P-brake bypass...) it also retains onstar and is pre wired for the ASWC steering wheel controls adapter (if you have them)
you will also need an antenna adapter that is not included with the kit
http://www.amazon.com/Metra-40-EU55-Antenna-Adapter-European/dp/B0007WW64Y/ref=sr_1_1?s=car&ie=UTF8&qid=1455694351&sr=1-1&keywords=40-Eu55
here is a better explanation of the kit differences

many options for adding remote start...
while for a remote start installer with a lot of experience, this car is very easy, for a DIY'er with little experience, it can be tricky as it is very different from most older cars.
one big issue is, that the manufactures that make the systems require any authorized retailers to also do the install and that is the only way they will warranty any of it.
a side effect of this is that most places that are not authorized retailers, have to acquire them some way other than buying them from the manufactures, and all too often the systems are refurbs, and the last thing you want when buying a system that offers no warranty is a system that failed and had to be sent back to be repaired/replaced.
having the authorized retailer do the install also not only gives you a warranty on the system, you also have a warranty on the install and probably most important IF something were to happen to the car while they were working on it, the shop should be insured to cover it.
I have seen some pretty poor RS installs in my days as a tech, and poor installs or install technique can lead to many problems not limited to but including frying thousand dollar car computers or catching the car on fire. you really should have some good experience with car installs before ever attempting to install something like a Remote Start system.