Warmth, humidity and a wide diet seems to be working for us over here. Our crabbies seem very well rounded and active and I don't do anything out of the norm for them. They are easy as pie but they're also sort of tedious, if that makes sense. They get coconut fiber in their water every day so that constantly needs to be freshened, and since the tank is high in humidity their food goes bad really quickly so...it's easiest to just change all of their bowls out once a day. Mine have four bowls
1 freshwater with a sponge
1 saltwater with a sponge
1 for fresh fruits and veggies,meats
1 for staple foods
I think, when it comes to activity levels, those really vary from crab to crab. They're all different. Our smallest and newest has been burrowed for over three weeks. I pulled him out to change the substrate and bathe them and he immediately buried himself when I put him back.
Another burrows every day and as soon as we turn the lights out- he comes out to eat and climb, so we watch him with the nightstand lamp on

"You can't escape our prying eyes"
The other two are out and active 24/7.
I think that if you set up the thirty for crabs, that would be awesome! We keep our four in a ten but it's a tight squeeze once you start loading in their huts and branches,extra shells and bowls etc.
The ten works, but if you have a 30, go for it!
Our master plan is to move ours in to one of those four foot shallow 30's I have. But that's a long time off.