for a 55 gallon, that would all depend on the particular species you want, fior sanils, i like the trochus, and we also have turbos, but the trochus, IMO are a much better snail, nad mybe 6 or 7 to start with, and see, as for hermits, i have no real idea, because i love clawless tanks myself
adn yes you should have no probs adding a new cleaner now,
HTH
,the name is fshhub, fsh=fish and hub=hubby(it was originally my wifes hobby when we started), so sir, boy or anything but maam, is fine, most say either fshhub or hub