Complete audio system upgrade

Hey guys, I'm about to upgrade my entire audio system with new components in the front, nice 6x9s in the rear powered by an Alpine multichannel and 2 12s powered by a 500w monoblock. I'm curious about a few things.

How are the acoustics in the car?

Will the trunk mounted subs (ported enclosure) fare well?

How bad is will it rattle? I'm trying to figure out just how much dynamat I'll need to get the best sound.

If anyone has done a full audio swap and done a dynamat sound dampening install, please let me know how it went for you. Approximately how much dynamat did you need?

Also, with the slide in license plate, how do you stop that from rattling? I usually used velcro tape on my other vehicles and just ran the screws through the tape. Works amazingly fyi, but for the Riv, I'm currently at a loss on how to do this.

Hi. I'm in the process of building my system (not the first one), can share some of my thoughts.
As for me, the rear speakers are totally useless, especially if you think of them as thin membranes dividing two closed volumes of air, in one of which you have your hard-kicking subwoofer... See where i'm going? I just removed my rear speakers and have no regrets ) Imho, it is better to focus on the front speakers.
Front speakers are 5.25" which isn't great. Even worse - speakers bolted to the plastic door cover, not the door sheet metal. I have really good speakers (Focal 130AS), they sound amazing, but, to my taste, they aren't loud enough. Not to say they aren't loud - just not loud enough, sometimes. I haven't decided yet what to do with that. One way is to choose louder speakers which almost definately will sound worse than my Focals. Probably I should find a way to bolt speakers to the metal, that would improve number of things including (hopefully) loudness. The other way, radical one, is to build custom "podiums" and fit some good 6.5" in there.
Now subwoofer. I have 400 Watt RMS 12" Kicker in a ported box and I pretty much happy with it. Don't know your goals in low-frequency department, but I guess your double 12"s would easily satisfy you.

Nothing rattles in my trunk or around it, and I haven't even started with the trunk sound dampening. Will leave it till both my doors are done. Frankly speaking, I doubt I will notice much difference (if any) after trunk sound dampening. But I will do it anyway, just to see if I was wrong )

No rattles really in the trunk, ever. The only thing I had to insulate was the license plate. I attached some foam behind it and it solved the problem. Mind you, I had two 12" DVC @ 2400 watts.

Make sure the subs are facing rearward (this is argumentative). I tried every which way to put my subs, and the best sound IMO was the box up against the back seat, facing rearward. I also installed two 4" ports behind the rear armrest to help get more bass into the cabin and also relieve pressure.

The acoustics are "eh". My Alpines in the front had adjustable tweeters. I had them facing up the most they could, and it helped. All that sound facing your legs just plain sucks.