I was very satisified with my Kenwood amp powering the 2 15s. I highly doubt 15s would fit nicely in a stang though, since I was using them in a Grand Cherokee. But now that I have a stang, I was actually considering putting a couple of small subs in the trunk (reduced trunk size with the convertible), like a pair of high quality 8s or even one 10. I'm definitely not into loud bass like I used to be, but I do want a little more punch. Oh, I haven't messed with amps since all my stuff was stolen about 5 years ago, just kinda gave up for a while, but I was impressed with the Kenwood line. As far as speakers for the doors, I actually debated that myself as well. After some research, I've decided on 2 sets of Kenwood Excelon series 6X8s. They fit good and I used to have a set of 5X7 regular 3 way Kenwoods that sounded awesome. So I guess you can't go wrong.
Check out crutchfield.com for specs, they have a great site, great tech support, and give you some free goodies, though I still think they are way over priced. I'd stay out of the retail stores as well, like Mickey Shore and Best Buy.
To purchase though, I'd recommend these sites.
www.hookedontronics.com
buyriteelectronics.com
www.etronics.com/
I haven't bought from any, but their prices look awesome. My friend bought a ton of stuff from etronics and had no problems. Hope this helps.