I've built up a list of the system I'd like to start building. I've decided to go basically all Alpine since they're a name I trust, and their quality is excellent. Let me know what you think of this set-up, and if there's anything I'm missing, besides a sub box.. I'm building a custom setup to replace the rear folding seat.
1) get a bigger amp for the component speakers. more power is always a good thing. plus, why did you pick a model that had the extra 200 watt channel on it? i would suggest getting somthing like 100x4. of course, alpine stuff is probably underrated, so you might be fine with the 50x4
2) how exactly are you building the sub box? dont put it in the region of the rear seat, it WILL sound like crap (well, it wont give you near 1/10th the performence of a more traditional trunk box). if you build it in the rear seat area, make sure it at least faces backwards toward the trunk. if you face them forward you wont be happy. ive had subs in almost every imaginable physical space in the car and facing in every direction, so trust me on this one.