This should not be a problem. If you know how, you can make almost anything you want with Game Maker.
The thing with the external project I would not actively call into life. But if someone would like to submit a concept to me or a programmer would contact me, it would be a possibility. I've had several people email me, but so far they've all been interested only in contributing art.
One thing you could do is a picture for the title screen. We could discuss this on discord.