Just found this thread! I have harris mud crabs in my 20H community tank. Started with 5, but lost 3 within the first two days. The other 2 have been fine for around a year now. They hide a lot and don't bother the fish, but they are ruthless towards the ramshorn snails in my tank... they just pull them apart then eat whatever isn't crunchy. The will climb up onto the heater, but have never tried to escape or seemed like they wanted to get out of the water.
I've read through your entire thread but I feel like it would be more fun to do a slightly brackish tank. If it wasn't for my riparium plants that I got I would be all for trashing my aquatic plants that aren't as tolerant and just getting some hardier brackish plants.
The Fraternity of Dirt #97Just because its dirt doesn't make it low tech