Glad you found a solution.
If you use ‘set target’, you just have to give it an actor reference, it automatically finds the camera.
Basically, don’t try and communicate with the Level BP.
All of this can be done, just with a normal player, and a BP with a camera in it. If you only want to show what that camera sees ( without movement, like a cut scene ), just use ‘set target’. If you want some control, make it a pawn and use ‘possess’.
Making the puzzle a level is probably not helping much :), you can put quite a lot ( like a whole room ) in a blueprint, and just put that in your level ( or spawn it ).