Hi! Welcome to the HCA, it's awesome that you are researching hermits before purchasing, great job!
So glad you asked. So. Here are all the care sheets, for basic crab care:
aaaaand basic crab care itself:
Anyway, in response to your questions:
For a temperature/humidity, 2-in-1, I use "Acurite Digital Themometer": http://www.walmart.com/ip/AcuRite-Digit ... r/16888914
Heat source, "Ultratherm Heat Mat", for a 10 gallon tank (for larger tank, use larger size. Heat mats should be place on the outside back of the tank, above the substrate line): http://www.reptilebasics.com/ultratherm ... -uth-6-x11
Wood-- do you mean for their climbing? If so, I use cholla from the Hermit Crab Patch: http://www.hermitcrabpatch.com/Cholla-C ... /cl011.htm
Oh, I guess that was the climeable material.... Whoops. Did you mean wood to build a case/ crabitat? Sorry!
I also use plastic vines from Petsmart-- just rinse/soak before use. You can pickup cheaper ones at Michael's or a craft store, but make sure it isn't scented or harmful to the crabs.
For substrate, most crabbers (myself included) recommend/prefer a 5:1 ratio of play sand (clean, undyed) and Eco Earth coconut fibre, usually the compressed brick form you can get at a pet store.
Make sure you buy a water dechlorinator and sea salt for pets at the petstore too. Most recommend Instant Ocean salt, and Seachem Prime dechlorinator. A small bottle is about $4 and can last virtually forever.
I think I covered what you asked... Hopefully I helped. Oh, and for cheaper options, for example, you could do a DIY coconut hut for a hide, or an empty, clean butter container, provided it's not clear (are there such things as clear butter containers??!!!).
What type of tank are thinking of getting? How many crabbies? Best of luck!
EDIT: Whoops, didn't see fantasybookworm's msg, lol. I use the Acurite digital thermomter, and it works, but be warned, the display will mess up. I kept it because it still reads accurately, but the temp display is screwed up. Don't know about waterfall/water features, I honestly haven't tried yet, but many use bubblers w/ great success. Oh, and sorry for the novel of a post.