2012 Prius three! subwoofer/amp/battery q's

I'm buying a 2012 Prius three from a family friend and I'm excited to put a new system in it. I have an alpine m50 and I'm installing a pioneer avh4200nex head unit and a jl 12"w3v3-4ohm. For now I'm leaving speakers stock but I'm planning on upgrading door speakers and sound deadening down the road.
My questions are... My amp will be pulling about 300 rms watts I have had a yellow top optima battery in the past, and it worked wonders.is that a good battery to run in a Prius with a small system? I've read a lot of posts about them and people seem to have conflicting views because of power output. I could use some clarification there.
If anyone else has the same head unit, what was your experience with retaining oem backup camera and ALL steering wheel controls?
When I do upgrade my door speakers what sound deadening material should I go with, what are good speakers for the Prius, and what's a good option for powering door speakers, I like the idea of the alpine power pack behind the head unit more than running another amp or buying a much more expensive 5 channel.

This is my first post on Prius chat, and my first Prius so I'm as much of a noob to Prius's as one could be. (Is it Prius's or 'pri'-i) lol

 

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