Everything is all about practice but knife edge is generally easier than prop hanging.
Getting the rudder movement direction correct is also obviously of key importance if you don't want to re-kit your model. The way i learned was by the rule that if the canopy is toward you the rudder stick moves toward the tail of the plane. If the canopy is away from you then the rudder stick moves toward the nose.
What makes knife edge easier to do is setting up knife edge mixes (KE Mixes) on your Tx. You generally need two mixes, rudder to aileron and rudder to elevator. The idea to to compensate for the natural roll and pitch coupling that most planes have to some extent when you apply large rudder deflection. Having the mixes set up means that when you perform knife edge your work load is reduced a lot.
To set the mixes just do a knife edge and see which way the plane goes when you add rudder. It will most likely either tuck toward it's belly or pull toward the canopy. Set up a mix off the rudder to apply elevator to compensate, some trial and error is always required. Same story goes for the aileron mix, watch which way the plane rolls when you add rudder and mix it out.
Some people think mixes are 'cheating' I strongly disagree. Assuming you have a computer Tx then these features are built in, you paid for them, you may as well use them. All the worlds top aerobatic flyers use mixes, so unless you think your skills are better than theirs then I say use mixes.
Hovering on the prop is quite a difficult skill to master. You would be better to build up to it by working on your harriers (high alpha). Use up rudder is key to both harrier and prop hanging (and to knife edge). Proper use of rudder is about the most important skill to master if you want to move beyond the most basic aerobatics.