You can look up poison frog terrarium and get tons of ideas. Their life style is close, just not as humid as poison frogs, but still rather moist.
Also I would suggest adding a dish of salt water, in nature hermit crabs take a dip in salt water now and then. Be sure to have fresh water available at all times. The salt water can be offered a few time a week, but not in place, of the fresh water. Just in a shallow dish next to it.
Next, flip that tank on it's side to give lots of vertical climbing space. Hermit crabs are "tree crabs" and love to climb up. You can add lots of branches and airplants or orchids attached to the branches. Also try adding some sort of textured background to the tank for the crabs to climb.
Last, search "Hermit Crab Forum" as there are many great forums made just for hermit crabs. They have galleries where members post beautiful pictures of their planted hermit crab terrariums!
Good Luck and keep us updated!