I'd get 8-10 snails that will stay small. Astreas will work on the algae on the glass and rocks, nassarious will burrow in the sand and come out at feeding time to eat the crumbs (assuming you have sand). I'd get only 1 scarlet hermit for a tank that small and make sure to have additional shells for him to change/grow into. I personally would hold off on any shrimp, as they seem to be more sensitive to water parameters and a tank that young is not a stable tank yet.