IS200s
I replaced the fronts only. The rears are oem on deck power. Not a fan of rear speakers as they provide rear fill only. If you run a setup with DSP that is entirely different, though. Music is typically coded as 2-channel stereo so rear speakers only serve those sitting in the back...
An 8 will fit in the front door
I am running the Focal IS200s in the door (plenty of clearance). A local shop fabricated an adapter which made install easy. Definately use sound deadening regardless of speaker size.
C2s
The JLs are a great speaker, ran the 525 in my 3. Prefer soft domes but the Focal tweet warms up once it gets some break-in time. Have found that to be the case with my home setup as well.
I used a JL XD200 which accepts speaker level input. JL makes an adapter to convert speaker wire to RCAs or you can hack up a pair of cheap RCAs and DIY. For the turn on I used a PAC TR4 (simple to install, 12V/Ground/+ Speaker lead/trigger wire to amp). Some people get noise with these, but...
The speakers are built into plastic pods, pita. A local shop is building an adapter to install an 8 inch speaker. The front dash left/right speakers have covers that pop out (the space is designed for a 3.5inch speaker and are prewired). Not sure about the center.