Does this mod generate tiberium deposits only on the starting world, or new ones you can visit through Space Exploration as well? I'm curious, since if it appears on all worlds it could make SE considerably harder, if you have to race against tiberium spread to mine out resources before they're destroyed across multiple worlds simultaneously.

It only appears where you've explored.

I don't know the specifics of how SE handles oregen.

I don't know the compatibility with SE, though curious now to try, but you can 'reset' any surface back to the original creation state by deleting the surface with the Universe Explorer. This would reduce the worry of the spreading.