Coding a 2D platformer is generally pretty easy, regardless of whether or not the graphics are 2D or 3D. My advice to you, SchokoKeks, is to ask a lot of questions and figure out exactly what kind of collision system you'll need to use, and then implement that system yourself. DON'T rely on the stock Gamestudio functions for much.

(in fact, although this would be a lot of work and require a commitment on Spike's part it would be beneficial to all parties if you created a tilemap editor for the game and used that tilemap data to perform simple yet accurate collision detections)