For about the people holding/not-holding towards the wall.... just have the kick-off wall's force ignore keyboard directions, and let the player's mid-air momentum come from what keys they hold once they're in the air? (Or, maybe a more obvious 'latch' moment would just make it clear that you don't have to keep holding the key... if people have a moment to hang there, they might be more likely to test things, rather than going "aah I'm falling" and going by instincts like I did at first...)

How would you reach the edge of the screen accidentally by jumping? It seems like putting in invisible walls to work around a level design shortcoming is a strange way to approach it, if I'm understanding right?