I have a green banded goby in my Nano that has great colors and a fun personality. I think it's listed in the link Tom provided in post #2.
I've also had clown gobies which are fun to watch and neon gobies which are colorful although not as much personality.
I'd go with one medium size fish that stays in the water column quite a bit like maybe a clown and then one or two nano fish like mentioned above.
Good luck!
Oh, or you could go with a small shrimp goby and a pistol shrimp. Those are always a fun choice because of their relationship with each other.
If you're not familiar with them, do a YouTube search and check them out too.