Also check out the pygmy wrasse (possum wrasse). There are three species with similar color and behavior, which do very well in small tanks. Though they tend to be less "noticeable" in the tank as they are more in and out of the rockwork. But supposed to have a cool personality if you're okay with a less bold fish.
In such a small tank, the territorial/aggressive behavior of fish like six-lines (and equivalent) is increased.
True Perc/Occelaris/Skunk Clown
Striated Wrasse/Springer's Damsel/Yellowtail Damsel
Blenny of some sorts
Goby of some sort but Probably a blue spot/yellow watchman OR A Yellowhead Jawfish
Cleaner Shrimp Pair
Pom Pom Crab
Rock Flower Nems
Maybe a BTA for the clown to host
Couple of hermits so i can entertain myself and guests with hermit antics
NO DAMSEL'S!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 99.9% people regret getting them because they are mean, Chromis are the only nice Damsel. Your clown does not need to host with anything. Your tank needs to be well established before you have nems, like a year-ish. Also dont forget most clowns are aggressive even though they are listed otherwise, its not usual to have a good natured clown. Your tank need to be up and running for 40-60 days to cycle anyway so you have plenty of time to decide on fish and coral. Also cycle it without the lights on as it goes faster and wont grow so much algae.
This is what Live Aquaria says about them (Chrysiptera springeri)
The Blue Sapphire Damselfish originates within the Solomon Islands, and is a brilliant blue coloration with black outlined fins. This species can quickly turn completely black when stressed which allows them to evade predators. Like many of the other damselfish within the Chrysiptera genus, it can become aggressive towards slower moving tank mates. Be sure the aquarium has plenty of live rock for territories and hiding."
If you want damsels get them but if you want other fish dont get them.