• More substrate. You can add it slowly & gently, about an inch at a time while they're down.

• Heat source - you canpurchase a heating pad for cheap and stick it to the side/back of the tank (not underneath)

• Deeper pools - salt & fresh you want them deep enough for your largest crab to fully submerge in but easy enough for the smallest to climb out of. Food storage containers are cheap pools and craft mesh works well for ladders.

• Reptivines are great decor and provide climbing and hiding opportunities.

• Additional hides - having multiple hides help prevent territory fights. I have a couple of terracotta plant pots turned on their sides and stuffed with moss to help with humidity

• Additional levels - you can create more space by adding shower shelves or similar - mine are moss pits and include foraging opportunities

• Foraging - I have urchin shells stuffed with foraging mix stashed around the tank - moss shelves.

• Shells - you can never have too many. They should be size appropriate and larger... turbo shells are pretty popular with most land hermies. Shell opening measurement is what you want to pay attention to. You look like you've got a decent collection of appropriate shells(depending on your crabs size)

Honestly though you look like you're off to a great start with a solid foundational set up. Beyond deeper substrate and pools everything else is gravy.