I still want to do a lagoon/dedicated anemone tank too at some point. A nice carpet anemone and just inverts and fishes that live in it, and maybe some sea grasses...
List of cleaners looks pretty good. I would avoid the
nerite snails, porcelin crabs, and pepermint shrimps unless you really need any of them. Nerites look like they can get into trouble, porcelin are crabs so I don't trust them, and peppermint shrimp can eat corals or steal food from corals by opening up the coral and pulling the food out through the tear in the flesh. If you have aiptasia, then fine, but if you don't, I wouldn't add them.
Also, how are you qualifying the difference between brittle and serpent stars? I imagine that brittle you mean the tan/brown/black striped ones, and serpent star you mean the green ones? The green ones eat fishes, don't add it.
I loved having a conch, they're really cool and eat all algae within the bottom 3" of the tank.
You'll just need to make sure the tank is really mature enough and has enough algae when you add these guys. I think you'll want to purchase maybe basic snails in the beginning, then slowly add more of them as time goes on. The conch and potentially stars can easily starve to death in a new tank (same with linckia star fishes).