Wow. Great minds think alike. My own platform game engine supports large tilesets, multiple tilesets, sprite packs (not yet loadable, but the framework is there). I was also considering vector masks (assuming you mean what I think you mean), but only for the events, not the tiles.

If you're doing your drawing with a 3D accelerator, it doesn't matter what the dimensions of the tiles are. The graphics card will scale everything as needed. It can be left up to the level designer to decide how big the tiles should appear on screen.

As I said before, I'd love to get involved. Back then I was in my final year of school, but now I'm in my first year of Uni and have all the time in the world