I own 6 hermit crabs, and am on a hermit crab forum. I love them so much!
You need at least a 10 gal tank, a heater (I recommend a under tank heater planted on the side, at least 6 inches of substrate (I recommend Eco Earth, stay away from calcium sand, or "hermit crab" sand), a hgrometer, a thermometer.
Temperature needs to be 70-80 degrees F. Some species though need it closer to 80. Humidity needs to be 70-80% though again, some species need it closer to 80.
You need at least a pair, hermit crabs are very social.
You need a lot of shells, different shapes. Not painted!
Finally, get creative. A lot of climbing toys are great exercise, and hideys are a must.
I think I got it all. Pet stores aren't very educated about them either. If you have questions, just PM me! =)
landhermitcrabs.com is a great forum as well as hermitcrabassociation.com