For example here is my CUC, keep in mind this is an astablished crew in a tank with plenty of rock and algae to eat, not a new tank. Also keep in mind these were added slowly over the course of a year not all at once.
1 sand sifting star
1 red sea star
1 lettuce nudibranch
1 longspine urchin
1 pistol shrimp
4 scarlet hermits
4 blue hermits
3 Halloween hermits
2 blue tip hermits
4 baby hermit (for the pistol)
2 trochus snails
2 astrea snails
2 spiney star snails
1 super Tongan snail
4 bumblebee snails
2 turban snails
1 fighting conch
1 emerald crab
1 pom Pom crab
Now here's where it gets tricky
From all of those we can break them down into 3 groups.
Group #1 just dump in the tank and never worry about
Group #2 they need a big tank or special care
Group #3 require special care/extra feedings
Let's start with Group 2, the sand sifting star, the urchin and the red star. These require much bigger tanks with a higher availability of natural food sources that my tank cannot natural provide. So, I have to manually feed all 3 each day or every other day and make sure they eat something. If I don't feed them they will slowly starve, just like fish.
Group 3,the pom pom, emerald and pistol shrimp. These again need to feed as the tank does not produce enough natural food for them. Feeding the emerald nori supplements the bubble algae they naturally eat which my tank does not have. Feeding the pompom mysis and krill keeps him from lashing out and keeps his anemones healthy.
Group 1 is everyone else, as long as there is enough uneaten food and algae the crabs and snails are happy. Even so every week I will give the hermits (specially the bigger Halloween hermits a mysis shrimp each.
As you can see its not all dump and prey, if you plan to keep alot of inverts be aware that some if not all require their needs being met by either your tank or your hand.