Looks fine with one caveat. Are you keeping corals? The angel could decide to eat them or any clams added to system at some point.
Personally, I stick with red leg hermits. My blue legs are always killers. To eat other crabs and the snails.
I would also go with some cerith snails. Great for everything! Since you have nassarius, you have sand. So conch are good too. Fighting conch are my go to usually.
Also, make sure to add the other fish prior to the clowns mating and spawning. They can become real nasty after that point to other additions. Mandarin would be fine, but angel could be issue or any other free swimmers (usually goby and shrimp will be fine).
Good. Luck!