lots of questions lol
why 3 subs? I use a single 10" fine and it's fairly loud. If I was you I'd go for a decent single sub in the boot and a set of components in the doors and tweeters in the right places. Save the money you'd spend on 3 subs and buy a better single sub. The size of your enclosure is so important. squeezing 3 in there limits your options whereas a single sub can easily be put in exactly the right sized enclosure.
I found using 6x9's on the shelf a waste of time when you run a decent sub in the boot. the sub will always win the air so the 6x9s can't operate anyway and damage themselves. They're alright on a strong shelf without a sub, but pointless when you start to get a decent system in there. if you really want rear speakers put them in the rear doors/quarter panels, but angle them backwards else the sound image will come from behind you and sound wrong.
Don't skimp on the wiring either. 4 gauge at least for the amp power cable and decent speaker wire goes along way towards a decent system. The cost of the amp usually detemins how good is it. forget watt figures. they just tell you how much power handling the sub or amp has. if another amp can produce the same volume (messured in decibels!), but with less watts then it says something about the quality of the amp. Genesis, JL, Audison, Diamond to name a few are the quality manufactures. Expensive though, but worth it.
Dynamat extreme is the stuff to use. the standard dynamat is pants and falls off all the time. Dynamat the doors with the speakers in and the tailgate. or if you can the whole boot.
hope that helps. of course I can only give my opinion. feel free to buy whatever you want
