I'm 13, so I hope I'm welcome to the young people thread as well lol.
May I suggest some scarlet skunk cleaner shrimp? I have a couple in my 10 gallon fowlr
, and I adore them! They are hysterical, and it's fascinating watching them jump from rock to rock and picking up food with their little white legs. They remind me of horses when they jump.
As for invertebrates, you can also get hermit crabs or snails. I've never been truly successful with hermits but I do have one left that is thriving. Snails are good for algae, nerites or turbo. My chestnut turbo snail ate up all the green hair algae that one of my rocks had on it when I bought it.
Firefish are wonderful fish for nano tanks. You can go with red, purple, or helfrichi. The helfrichi is absolutely gorgeous, but extremely expensive. I'm getting a purple one for my tank (It's pretty new).
P.S. I agree with you. The symbiosis between watchman gobies and shrimp are amazing!