You have to wait until Winter (April, August and December) where snow drifts will appear, allowing you to climb up to previously inaccessible areas.
Both are acceptable, but you normally say at the top.
go through the oreburgh gate. take a Pokemon that has a rock smash, surf, rock climb, and strength with you. go north from the entrance, then surf east, continue walking east, climb the rock wall and...
as far as my information goes not none of the m let you play as a roll in the gym srry i think it would be cool to.
Gym is short for Gymnasium which is from Ancient Greek - gumnasion - "exercise, school".