1) if you are sure the engine is OK again, why not give it a try?

2) Yes, the clutchbell must run free, the clutch will only engage when the engine is running a certain rpm not the clutchbell.

3) a lot of rpm and less speed can be:
a) bad clutch
b) bad (adjusted) slipper clutch (the spurgear)
c) bad gearbox. (will not shown a slipping engage)