WonderfulFel.. is right -- often colors don't cover and multiple
coats are necessary. The darker the color, the more coats needed
typically.

Floetrol won't help much with coverage - it's used to slow dry time
when doing trim/doors/windows. It also allows the brush marks to level
out, letting latex act more like oil.

Oh, and no, a sprayer is not reasonable for a room or 2.