For four plants, you've probably got enough light...around 17000 lumens total. That will work for 3-4 sq. ft., and that's what the XS is. I'd keep all but one or two CFLs on top; canopy light is more important than any other light. You've got light to flower at least 2-3 of those plants.

I've had problems with MiracleGro soil. Even the organic stuff has been lousy for me...very acidic. Other have done fine with it, though. Make sure you check your pH regularly with the MiracleGro. And don't start adding nutes for at least two weeks.

Sounds like you're off to a good start. Good luck!