quick opinions
.... anyway...
I would say, stay simple and straight forward. Buy a 5 channel amp (so you dont have to futz with multiple amps) - replace the stock speakers with upgrades, keep your double din idea -- and get a dual VC sub (single) if you like such things....
the bottom line - with a modern day 5 channel and decent replacemnt parts you cannot go wrong. Don't shirk on the install (get high quility wire and pay attention to run power and signal seperate)... you should be happy to listen.
I have a civic, and I run:
Sony Explod head unit (I dont like it but it plays MP3's and cost 80 bucks new)
Alpine V12 4 channel amp (for mids and highs)
2 Alpine RD 5 1/4" fronts
2. Polk 6 1/2" rear
Kicker Z120 (for the sub)
2 dual vc 10" subs
I got it all used - and it's way too much for the small space of a civic.... have fun and tell us what you ended up with~!