Steel studs / Basement Insulation

I just bought enough NEW 3 5/8" steel studs and track for the entire basement at a steal form Habitat for Humanity.
I plan to frame and insulate the outer walls only, within 6 weeks to get an energy rebate.
Several questions,
When I space away from the wall, is there a way to use more than R 13.5 fibreglass insul in , not compressed of course?
Can I use R20 and let it hand out the back without collapsing, or is there a way to support it to keep from sagging or is spray foam or rigid in behind my only other option.
Second, if I spray foam, then obviously no air gap, but can I spray over a wall with a fine crack / leak which is caused by bad drainage outside... in a window well. The drainage is being improved as I plan to excavate the outer wall and clogged window well to seal at the same time.
Any other pointers for lapping corners , etc with steel studding would be appreciated.