Kicker is quality gear...but unless it also came with replacement door and rear deck speakers, I think you could do better for $1200. A good 5 channel amp, sub (8" or 10" w/enclosure) and upgrade the existing speakers would be 1000 X's improved over the base system, then upgrade the H/U at a later time or vise/versa...depending on what is higher priority for you. I would consult with a reputable audio tech and see what they can put together...there are so many choices that it makes it hard to decide which way to go
Any further developments on an interior choice?? This will be my new interior (should be delivered mid next week) Black leather w/ granite suede inserts...not a bad deal for $700
The Kicker Soundgate set for 1200$ would come with door speaker amps not sure about rear deck, and the sub in the back. Also nice cause it's all plug and play since it's specifically designed for the Mustang. I think I'm leaning towards sound more than the HU area, since I'm pretty sure Sync is practically unreplicable, and I can live without Nav(I have an iPhone that can do the job for now) and Back-up camera(guess i'll just have to use my eyes :P). And okay, I'd just have to find a reputable audio tech xD and yes, many many choices.
Interior wise, I have chose to spend a little less than new seats would cost me on other modifications so I have enough left over to buy presents for my family for Christmas. So I'm getting a spoiler/scoops/window tint for now, and will upgrade seats early January along with the sound system unless I change my mind. I will have a lot more money then than I will now. I was planning on just base premium seats for 550$, but what you have shown me has me considering red+black seats since I love the red+black combo, I guess it just depends on what it'll cost in comparison and if I can find it.
Mtu, to clear up some of your questions: I listen mostly to Heavy Rock/Metal and such. I care more about bass, a lot of bands make use of bass drops and I'd like to be able to hear/feel them. I wanted my head unit to just be a little more high tech, offer things such as sync/nav/back-up camera and not for sound as much unless that'd be a better option. I'd probably be using my iPhone and music off of it for audio, so yes to audio-in. I hope that helps as much, since I don't know exactly how to answer your question about vocals, a lot of music I listen to is either acoustic singing or lots of screaming. Not sure if that helps.
PPinTX: I also don't like the drab of the interior on the base model
I actually love the door panels along with the speakers of the premium models. I looked into replacing the door panels, but it is around 1600$ for a set of both premium door panels and I am just not willing to pay that when I could do so much upgrading for that amount, instead of just replacing.