Welcome to the Sanctuary!
2 small fish would be the max. False Percula, True Percula, Royal gramma. Basically anything that doesn't get over 4 inches is fine. Stay away from damsels they are mean and will harrass any other inhabitants in the aquarium.Astrea snails, nassarius snails, are good janitors that stay small, turbo snails get too big for a nano in my opinion. dwarf hermit crabs, though witfull will say they are evil, and I'm starting to agree.
I have a 12 gallon nano, with a false percula, Royal Gramma, 10 nassarius... I mean 5 nassarius thanks to my hermits. 6 dwarf red legged hermits, and 2 astrea snails. varius zoos, mushrooms, anthelia, and a cabbage leather. I would also recomend getting a protein skimmer. I use a CPR BakPak IIR, but the Aqua C Remora also does a good job. Otherwise you'll be doing a couple water changes a week. I still change the water once a week, just to be safe. You'll want the water flow rate at about 10x the volume of your tank, minimum.
Peace
EK