you can do that ! I would avoid any type of sand sifting stars as they would most likely die of starvation
I keep lots of different inverts in my tank
I have a 90g tank lots of rocks , it keeps everything apart as they all have there own place not everything listed is compatible for a 30g because of lack of room would most likely fight , this is what I have
1 pink lobster about 6 inches
2 skunk cleaner shrimp
2 fire cleaner shrimp
2 coral banded shrimp
4 peppermint shrimp
2 pistol shrimp
6 serpent star
too many to count snails assorted types
too many to count hermits assorted types
3 nems
6 sand fleas
2 porcelain crab
6 emerald crab
1 pompom crab
1 decorator arrow crab
12 feather dusters
3 coco worms
you couldn't keep everything in a 30g
you would need a good amount of rock for everything to hide and Rome about
no the lobster gets to big for a 30g so he is out
some of the shrimp listed would get along in a 30g but not all
only 1 type of crabs would get along with hermits in a 30g my favorite is the pom pom as he comes out more
1 serpent star
1 fire shrimp
1 skunk shrimp
20 assorted hermits
20 assorted snails
4 feather dusters
2 coco worms
sand fleas need a deep sand bed plus they are hard to keep alive
this should give you a idea of what you can keep