I think that is way too many crabs, and I know a lot of people on this board feel the same way. I have 4 scarlett hermits in my 55 (lost one) and that number is just fine. I would recommend a few hermits personally, because they are fun to look at and don't seem to cause any problems in small numbers.
I agree with the above posts about getting a variety of snails if you can.
I have 10 cerith snails
4 trochus
2 turbos
1 astrae (hitthhiker)
3 urchins (hitchhiker)
Along with the 4 hermit crabs. I get algae along the walls of the tank which I need to clear off, but that is it.
I agree with rumonov if you can find those snails, get some. If you want to have a snail population that replenishes itself, it might be a good idea to not have any hermits at all (I am not sure about this)