C.C.
We called him "Hermie". We loved him.
Hermie lived for a while, but just in the stuff you describe - the stuff our pet store recommended.
Your heart is in the right place. Good luck with the other two.
To bring some smiles into your house, check out these books (I liked them bc of the "Hermie" name):
http://www.hermythehermitcrab.com/
And this one for information:
http://www.amazon.com/Hermit-Barrons-Complete-Owners-Manu...
And the Mamapedia of Hermit Crab owners:
http://www.hermitcrabassociation.com/phpBB/viewforum.php?...
http://www.hermitcrabassociation.com/phpBB/index.php