Get the last Mag36 from rivD. He only wants like 75 for it. and you can split it and run one outlet on one end of the tank and one on the other and the length of outlet pipe and bends will slow the flow down to about 2600GPH or more. Depending on how long your return lines are.
I would just do a very light layer of PF sand it's cheep and looks nice with rays.
I just did 3 400watt theo heaters in my big tank. it's more then enough so think in the ballpark of 1k for heaters. I know the theos are not the best but I got 3 of them for less then a 1k titanium w/ controller.
I would be most worried about mechanical filtration os your sump setup for filter socks?