I feel its too small for a dm past three players. Expand the island slightly and add another structure or two to fill up probably 1 64x64 baseplate so players aren't fighting in such a cramped space.
Yeah, this has been one of the problems. I'm considering adding some more plants to the island and making it bigger. One reason I made the glass break on impact was so the space can change quickly from smaller to larger. Not to mention would be a neat effect when playing with pushbrooms.
It's a simple build, and I think you should connect this lighthouse to a road which leads to a city on another island. I think this is great!
Neat idea, but I might keep it simple. However if I do use this build in some other idea with a city, I'll keep this in mind!