The backfiring into the intake/airbox would indicate that the intake valves were not closing all of the way, so the combustion was escaping in that direction. I would check the tappet clearance - if the clearance is too small, the intake valve(s) could be hanging open slightly, which could be causing the lower value on your compression check. Make sure you are at Top Dead Center when adjusting.
As far as the oil consumption, it could be leaking out of one of the drain bolts, so check the sealing surface for anything wierd like debris, and try changing crush washers. If its not leaking out of a drain bolt, then it must be burning - meaning that the oil is coming past the piston rings or valve stem seals.