Three 20 lb bags - looks to be just about perfect.
Just got some plants in the tank today, so will take a little while to see how the lighting does. Coverage seems good (except for the back corner, as expected) but right now it doesn't seem as bright as I was expecting, but the driftwood is leaching tannins like there's no tomorrow so the water isn't exactly clear. I put some carbon in the filter and did a PWC today, will continue PWCs until the water clarity gets better. After that I can give a better assessment of the lights.
I had this tank set up for about 3 years with no obvious circulation problems with the XP2 (by "no problems" I mean no areas with accumulations of crud, and no BGA or other algae indicating low flow). The CO2 diffuser is a small powerhead which I usually place in the back corner pointing towards one of the front corners so that helps too.