On the latest map, the pair of craters in the NW look a bit too "regular" I think.

Fallien should probably be all shallow sea inside the bay/lagoon, unless your story says otherwise of course. With the inland sea, you might make some parts rather shallower, like the real Caspian sea which is very shallow in the north, deepening to about 1000 m in the south. Varying the width of the continental shelf for the mainland would add some interest and realism.