If u like hermits and u want enough to do the job efficiently and properly, don't be afraid to up their numbers a bit... anytime I have kept them and had live rock in my display (I have none in my display now) I have used 1 per gallon... not that I buy into the whole "per gallon" rules for most of anything it seems to be applied to, I jus find it to be a good starting point... until my last upgrade, when I kept a 40 breeder with a fair amount of live rock and fish for the water volume of my system, I used appromately 45 hermits to keep things clean like the surface of the sand and rock and all the rocks crevices... however, like stated above, make sure u have plenty of extra shells, or they will start killing each other...
Jmo, nothing more...