I have red crabs... Don't knwo what species...

They are doing fine so far. I put 1/4 table spoon salt on every 25%
water change on my 33gal tank.

And yes they will want to get out of the water so you should have
something that sticks out of the water that they can climb to.

On my pnated tank, none of my plants reaches the surface yet so what I
did is to put a 4X4 wood and attached to it one fo those garlic meshed
bags and make sure that it is entrenched in one of my plants.

That way the crabs can climb the plant and the meshed bag to the top of
the wood.
Works great, theres always a crab there sunbathing. :)