The only invert to avoid really are the ones that are dependent on sand for their survival. Examples would be Sand Sifter Starfish, Tiger Tail Cucumber. Just consider how they live and what they eat to decide if it's wise to add or not. An exception would be a Nassarius snail. They do burrow in the sand, but with no sand they will just chill in the corner or in the rockwork but can still survive just fine. The rule of thumb would be the same for BB as it would sand. For new tanks: 1-2 snails per 10 gallons, 1-2 hermits per 10 gallons. Don't fall for the trap of "CuC Package for X gallon tank" that has 100 hermits and 100 snails. Most would be dead in a short time.
As the tank matures you can add more CuC slowly over time to meet the demands of your tank. Serpent Stars are one of my fav for eating leftover food and are fun to watch walk around. Good luck.
