1. Yes, I'm quite please with my EZ Amp. Install is a snap.
2. 100s of choices: Sundown E10, Incriminator Audio I series, JBL GTO, Image Dynamics ID10, etc.
3. You should be able to. I did for the 430N. I don't know the difference of the 8.4an. Use the bare-wire-to-RCA jacks that come with the JBL amp.
4. I'm also unsure if the colors changed in '13. I'd search other forums. I'm quite positive colors will be the same between all platforms using the same audio system. You may be able to find the wiring diagrams here:
I did for my 430N system. Colors were identical.
5. Buy or build a decent box for your sub. I'd advise against the 5/8" MDF ebay ones.