suggestions on tank mates

[Lt.]

I'm not getting anything bigger, it's all gonna be peaceful schoolers and shoalers in the tank. I was gonna keep my Australian Rainbows, but their more aggressive to my other fish than I thought they'd be, so there going away.

 

[Lt.]

Ok, so I have around 20 ghost shrimp, 4 zebra and one leopard danio, 10 rummy nose terra, 4 von-rio tetra, and 3 pepper and 3 bronze cories. Can I get a fiddler crab? What special care would it need?