The tile property data is stored inside the exe. Too bad I don't know anything else about that. There is however CK Guy's tile editor somewhere..BTW is there any information regarding the tile data? For example how does a tile block your movement, how to make it a secret passage tile, etc? It'd be nice if I could edit that too!
About the limits, probably something like 200x150 starts to be maximum. Not really sure, can't remember whether adurdin mentioned it once or am I just making things up.