Quite ambitious. But I must say you're not going to be able to go too far with Game Maker, at least not in the "hundreds of objects on screen" department. Trust me, I've already tried this in 
GM6 and even before 100 objects are onscreen the game 
will slow down.
Plus GM is an 
interpreted script game engine, which means half your processor time is wasted finding out 
what to do before even 
actually doing the operation. Game Maker is really best used as a learning tool, not for a serious project. 
(This is why the Delta Project is where it's at today - there is no way GM would ever be able to handle the DKCLB's absolutely massive feature list.)Also 
in my opinion you need to have a way to deactivate off-screen objects or this won't get anywhere (since all objects in the level get processed by default, it will cause immense slowdown at some point).
Good luck, you'll need it. 