I would hold off on the shrimp, they tend to be not as hardy to new tanks. Id wait another month or two on them.

As for snails, once your alk is stabalized, i'd go to start with 5 Caribbean Nerites, 2 small nassarius and 3 crabs. I'd then wait and see how well they keep everything maintained. If after a few weeks you think you still need to add, i'd add the cerith snails. Having different types of cleanup crew enables you to have good coverage.