My son and I are new crab owners and this community has helped so much, so huge thanks from us!
I never thought we would have hermit crabs... But the story goes - a couple of days ago we went to the beach (and because I have a broken foot I sat on the bench waiting for hubby and son to go play). They came back with a couple dozens of marine crabbies and little man wanted to take them home. I looked up on how to care for them and went and got a 10 gallon tank thinking most of them will die off
I stayed up all night doing research and found out that marine crabs need different habitats than land crabs. I realized we will not be able to care for these marine crabbies so I did my best to make them as comfortable as possible till they passed. We were left with a kit for hermit crabs so we bought two hermit crabs from the store as I read they need buddies to play with. We have name the slightly bigger one Ozzy and don't have a name for the other guy yet.
Currently I use mix of eco-earth and play sand for substrate. There is a coco hut, salt water and fresh water dish, shells, as well as some climbing toys I made with pear branches, grapevine and netting (can someone tell me if pear is ok? I've found yes and no answers). So far I've found their favorite food is coconut!
They are shy (and probably stressed from being accidentally dropped, so now we don't handle them) so the first couple of days they have been burrowing during the day and came out at night time. I like to think they now have a better life than in the pet store and am looking forward to see they grow big and healthy. 
