All looks fine. As Finatic mentioned adding extra shells can curb the amount of smails that hermits try to take the shell from. Do you have a sand substrate? I ask because the nassarius snails do best in it.
General rule of thumb fo
snails and hermits is as many as 1 per gallon of each. I usually do not go more than half of that.
Try updating you "My info" section, so we all know a bit more about your setup to include equipment and current inhabitants so we can better give advice.
I assume this is a newer setup, any fish yet? Are you do FOWLR
or reef? You will need to watch fish selection as some like to munch on inverts. As for emeralds usually 1 per 30-50g, but not knowing how big a setup you have I cannot comment.