Congrats on your new tank!! I've had this tank for almost 2 years and I love it. There are a lot of fun nano fish you can put in a tank like this without needing to add any damsels or clowns.
I personally love Firefish - they're gorgeous no matter which type you get, which can range from very inexpensive (Red Firefish) to very expensive (Helfrichi Firefish). I have red, purple & Helfrichi and all 3 types have been very easy. Also, Royal Grammas are very pretty fish which tend to be pretty active. I have a couple of Blue Neon Gobys as well & they're cute, small and like to clean larger fish.
While I have never bought from them, Live Aquaria has a pretty good list of Nano compatible fish & they're all pretty interesting.
I have a High Fin Red Banded Goby and a Tiger Pistol Shrimp in my Evo right now. They're a fun pair to watch & if that's something you're interested in, a smaller tank is a great option. You run the risk of not seeing them much in a larger tank but in an Evo, you'll definitely get to see their fun relationship.