Alrighty, let's get to it...
1. Alpine headunit. since you got the money(not hatin') go for the gold. get one with a fold out screen as well as a DVD player.
2. I would suggest alpine type R components for the speakers. i dont know if the 3000GT is has coaxials or not, but guys help him out with some speaker suggestion.
3. get a highpowered 4-channel amp for the speakers. uhh rockford, profile, those are really the only ones im familiar with
4. SUBS.....the component that brings the system together. Stick to resonant engineering
http://www.respl.com great company. Now since you didn't give us specifics, we need to know if you want ANY use of your whole trunk, if not....well then I'd say go with 2 RE XXX 15" with a hifonics brutus amp running to each(i dunno what amp you do have, but the XXX will eat power.
5. could could keep going.... fiberglass the whole trunk, throw in an extra battery, you'll definately need a couple of caps when pulling THAT much power.
- with that much money get creative. but in order to fine tune our suggestions, we need to know what type of music you like to listen to. if you want mainly LOUD or sound quality, or somewhere in between. when you want advice you're in the place to be.
PS - if you have any ?'s PM me.