Instead of a couple of 2ch. amps, I would suggest 1, 4ch amp for the reg. speakers, plus a designated amp for the sub. Too many amps makes it kinda, sorta, difficult when setting up the cross-overs. A 4ch with a 5th channel for a sub can work, too, but I've yet to see one that works well, without costing an arm & a leg.
When building interiors for my customers that are going to install a decent sound system, I like to put down a coating of 'Lizardskin' on the floor all the way up the firewall, & in a GMT400, the back wall, too. I'll follow that up with a layer of 'Fatmat', which works just as well as the name brands, @ 2/3 the price.
About 65-70% of road noise comes through your doors, so I put a layer of the 'Fatmat', on the inside of the outer door skin, with another layer between the inner door & the door panel.
For the ceiling, I've used one layer of the deadener, but I've heard of others putting 2 layers up there. Don't know how that effects the fitment of the headliner.
When the vehicle has this amount of deadener, your system doesn't have to work as hard to fill the interior with sound, or to overcome the road noise. Medium range systems sound will sound great, high end ones will sound amazing.