Multi amps, caps, crossover questions.

What's the proper way to set this up...
radio has 3 rca outputs, front, rear and sub-woofer.

- Stinger 1.4 cap, big enough for JL Audio 1000/1 v2 ?

- Gravity 5.0 cap, big enough for multi amp setup ?, they are:
JL Audio HD600/4
JL Audio HD600/4
JL Audio HD750/1

- JL C2-525 speakers, do i need to hookup crossovers or are amp filters enough ? (600/4 amp)

- Alpine SPR-50 speakers, do i need to hookup crossovers or are amp filters enough? (600/4 amp)

- Speakers for HD750/1 amp, 8" for vocals, any recommendations ? to be door mounted.

- speaker cables, could I extend them ? about 2 ft max.

- RCA connections for HD750/1 amp, it used to be my sub-woofer amp, but planning to use it for vocals, should I split rear RCA signal and share betwwn 2 amps without degradation ?

thanks and sorry for all this questions.