Yea I've never gone with a live planted tank before, maybe this will be a good place to start. I put gravel in because I had some laying around, do i need to use a special sand or dirt for live plants?
Crabs? Could make a cool crab tank with an interesting piece of drift wood. Crabs balance themselves seeking brackish and freshwater as they see fit so that would help with environment management.
You would definitely have to watch the water parameters.