You can mount your car amplifier in the back floor or in the trunk.
A good place is either in the trunk, or under a seat so it is out of the view of thieves.
Yes, you can mount it any way you like.
You should get a amplifier if you want good sound quality out of your speakers.
Getting good music in the car is up to you, depending on what music you like. But if your looking you good sound in your car you will need a car amplifier.
What do you mean charge the amplifier? It's not a battery, so you just turn the stereo on. When the stereo goes on, the remote wire will turn the amplifier on and you're good to go.
There are few reviews but the are fairly good ones.
The Kicker ZX300.1 Subwoofer Car Amplifier is great.
The trunk of your car is the best place to mount a pair of subs. The trunk also acts like a sound chamber for the subs. Just make sure you seal the trunk good so it will not raddle when the bass hits.
It is a good mid range amp.
A 5000 watt digital monobloc amplifier is good for competition cars. The ICBM Giant 5000 watt is a favorite right now.
Depends on the output of the amplifier.