Next phase of Audio Upgrade

So next phase of my Audio upgrade is to amp door speakers.

Currently I have:
Head Unit - Dynavin N6, RCA outputs in the back :) http://ift.tt/1JC3lIL

Front Door Speakers - Rainbow IL C4.2 Speakers + Tweeters
Underseat Subwoofer: MB Quarts
Rear Speakers: BMW Individual
Boot: JL250/1 mono amp with JL250 Subwoofer

The existing amp only powers the Subwoofer in the boot. None of the other speakers are amp'd.

The following amps I have shortlisted so far:

5 Channel, so I could get rid of my existing JL250/1 mono amp
Rockford Fosgate Prime R600X5
Kenwood KAC 7005PS

4 Channel to run alongside my existing JL250/1 mono amp
JL JX400/4

I'm a right noob when it comes to car audio, however I do like challenges :cool!:

Here are my questions:
1) Do you see any problems with the amps that I've shortlisted?
2) I'm falling towards the RF amp, but what do you guys think?
3) Plan is to run RCA cables from the back of the head unit to the amp and then from the amp to speakers, this is how it's done, right?
4) Anything else I should know?

Thanks

Next phase of Audio Upgrade