nope thoose are true fiddlers, they will drown in over 6 inches of water. they need just enough brackish water to get their gills wet every now and then. in the wild they live in burrows on the mudflats of the mangroves. when the tide comes in the climb up mangrove roots or stick it out. then when it goes out they go nuts over the mudflat. sort of like mudskippers.
They like sand too. They burrow in it and feed off of the stuff they find in it. I would also be lying if I said they didn't need a larger enclosure too.
We have kept them in the marine lab, they make great pets!
Hmm I don't really think there's a rule of thumb, but I would say 10 gallons would be sufficient for up to 4, maybe 5 with the proper setup. Fewer males than females of course. The males have the single large claw.
If you are going to collect that many from the wild try and set them up correctly. Sand and brackish water is a start with a "beach" type area with driftwood would be ideal. You also might want to take some vids off your youtube page if you are going to advertise it. You have vids of dead fish being kept in horrible conditions.