Well it really depends what you are looking for. If you want all around loud but clean sound the best bet is to go with two amps, one to power the interior speakers and the other to power the subs. As far as head units go, just make sure you get one that has alot of expaning options, but it really depends, do you want a cd or mp or what?

There are alot of brands you can go with but make sure you dont cheap out, cause it not worth it. For subs alot of people recommend JL or and personally for interior speakers I like Infinity but alot of people know more than me so wait to hear from them.

Ask this in the Audio forum you will get alot more help there.