Next fish to add?

[Nano]

I have a 20, and if some of you have been following my threads you'll know I had a salinity spike this weekend, which is now under control, you'll also know my clown had ich (or so we thought) It turned out it was just sand, but I am still treating the tank as if there was a case, just to be safe. So I know its going to be 2-4 weeks before I add anyone to my tank, but I need some opinions haha.
My tank is 20 gallons, with a 20 gallon sump, I have one ocellaris, a skunk cleaner, 2 hermits, one emerald crab and 2 snails. My ideas are as follows

6 line wrasse, I know I'd like one of these for sure
Some possible Ideas (no I'm not doing all of them lol)
yellow watchman goby
scooter blenny
bi color blenny
and thats all I've got. I'd love to have a green spotted target mandarin, BUT I dont think my tank would support him. (a guy can dream though right? lol)

any further suggestions? I'm looking for additions that are colorful, but also serve a purpose in the tank i.e. eating algae or nudis etc.