Dwarf Zebra Hermit Crabs

[Drfu]

I have been thinking of adding some crabs to both of my nano tanks for a while now but have always been worried about them munching on my cuc. I have read online that of all of hem a dwarf zebra would be the best for small reef tanks, one is 8 g & the other is 15. I would like some input on this species as a choice and have some questions:

1) is this a good choice for these small tanks?
2) where in Calgary does a lfs have these
3) is there a rule of thumb of how many?
4) i know you need to have some extra shells laying around, any particular types of shells?