Honestly, they're not hard to take care of. Ours were fine with gravel and without a humidity guage. They're tank was a decent size, but we let them out at least every second day. Me and my brother would make like a maze out of corks and watch them run though it (or just knock down everything in their path). We had the three different bowls, we fed them, etc.
They ended up dying because they didn't like the shells we picked out. We had at least 3 per crab, but they didn't like any of them and ended up dieing after a few months.
I think they're like goldfish, you don't expect to keep them long term no matter what you do to take care of them.