How many enemies is appropriate per level?
I am not sure but depending how powerful they are, three would be a good amount to test.
Would you prefer a HUD?
I don't believe a HUD is necessary unless there is something that we would need to look into.
How strong should the enemy attack the player?
I think they should be a minimum powerful where it can be dangerous with interaction and drop great items.
How should the player attack? Would you like mouse click combat or full keyboard combat?
Mouse clicking would be better in my opinion.
How do you feel about the jump height/power? Should it be lowered?
I believe the jump is good the way it is.
-Alejandro