Aftermarket radio and amp questions

Hey guys! 👋

I am installing a new sound system in my 2011 Aveo LT. So far I replaced the pillar tweeters, the door mid/tweeters and plan on replacing the rear deck and adding a shallow subwoofer.

So, I installed the Binize 10" android radio and spliced the aftermarket radio wires to the wire harness adapter and it seems to be working, but now I want to amplify it all so I am considering this amp:

https://a.co/d/h1Bm0pc

And this subwoofer, either this or an under seat:

https://a.co/d/2aYJK12

I am buying the Crutchfield 9 in one speaker wire as well..

What I would like to know is

1. Where should I put the amp? Under seat, trunk or somewhere else?

2. How do I run the amp 12v, ground, and "rem" through to the battery? I have no clue.

3. I'm not looking to rock the neighborhood but I want some quality sound in my car so I replaced the pillar tweeters with a couple Rockford Fosgate 1"s and the door has a couple 4" kickers. What should I get for the rear deck? Is the sub I'm planning on buying to powerful?

4. Can you recommend a reasonably priced amp/sub that may sound better

5. How should I soundproof and with what?

6. Is this right? Aftermarket radio speaker wires disconnected from wiring harness adapter and reconnected to the 9 in 1 which in turn wires into ch1-4 of the amp which sends the signal back to the radio through L and R AUX input on the radio and viola! Speakers are amplified, then when I get the subwoofer I wire the sub to the amp (not sure which channel to use) or do I wire the subwoofer to the radio subwoofer outputs?

Thank you so much for all your help!