I am getting back into the hobby and am starting a 20g nano. I personally am staying away from any crab this go around so I don't have to worry about them being aggressive. I will probably start with only adding 3 nassarius snails to help keep the sand bed clean and agitated. Other than that I plan on being the clean up crew! Don't really care for inverts messing with my corals either
You will want more snails then that. You want to mix it up because they all eat different stuff. I have a 16 gal and have 6-8 small sand sifting snails, 3-4 nerite snails and about 6 cerith snails. I also have a few blue leg hermits and accidently got a zebra hermit, that guy is awesome. He doesn't bother the coral and he's all over the place. I also have a huge turbo who cleans great.