I have an 8 gallon that I keep a small blue damsel and an emerald crab in. I have a larger tank that I will put the damsel in when it gets to big then I will probably get a small goby and pistol shrimp.
This is a guide for nano fish lgreen's Ultimate Guide To Nano Fish - Nano-Reef.com Forums
I don't agree to all the fish in the size tank they recommend.but it is a good start to researching.
The more water movement you have the less problems with algae you will have.
Don't always trust the LFS
I am lucky I have 4 in the area that is really very good.