Do not get a tomato clown unless it is the only fish you'll ever keep in the tank. They are remarkably aggressive and will fight and kill your other fishes, particularly in a nano.
Next purchase? If you're going to the lfs to get your water tested, buy either an api saltwater master kit, or some salifert test kits. You only need ammonia, nitrate, calcium, and alkalinity. Then buy a refractometer from eBay or wherever else they're only <$50.
Probably too many snails, particularly with the Mexican turbo snails. They get huge becasue they eat a lot, but your tank won't have a lot for them to eat.
The chromis, I would make sure you have a lid on your tank for them. I love them, and have had them before, but know that they'll pick each other to death slowly (they're not actually schooling fishes, they're hiding fishes, when left with nowhere to hide, they school, as they do in our aquariums, however they get angry and aggressive when kept like that and end up killing each other. They are damsels after all).
Sorry to be a Debbie downer, but just trying to save you from the headaches and heartaches that I've already been through (all except the snail one).
