kbaker......just realized that you are also looking for power supply help.
Class D amp is a great way to go, Capacitor is a must (bigger rather smaller), naioa.com discusses "Big 3 upgrade": 2-ground wires on chassis, and run a 4 gauge straight from alt to battery.
Long story short. I had 800watt fosgate amp, bridged, to run 12" Kicker Solobaric, lights dimmed real bad. ((My stupid mistake fried the fosgate, bought a Kicker1000.1 (750.1 supposed to be made to run sub, should have bought 1500.1) ))))) The Kicker makes more power but because it is a Class D amp, my light dimming has virtually ceased (only minor under dash light dim now, very minor). With the power that you are going to need, investing in some charging system help is a must, you shouldn't need a new alt though with the other system helpers avail.