That seems like pretty heavy stocking. Manageable with great filtration, an oversized skimmer, thoughtful rockscape, and luck of the draw on everyone deciding to play nicely. I currently keep two ocellaris and a cleaner shrimp in my 20, and have no intention of adding any other fish. This keeps my bioload extremely low, which is perfect for me because I don't want to have to do maintenance every couple days. If you're thinking of paring your list back a bit, I would personally cut the YWG/shrimp. I had a YWG in my first reef tank and saw the tip of his head maybe once a week. Not worth the addition to the bioload, and he was a pain to catch when I gave up and took him out, had to pull all of my rockwork. If you want something that will spend more time in the water column, the firefish is a good choice. I'm a huge fan of clown gobies, they have great personalities and are easy keepers, spend most of their time hanging out front and center on the rockwork. Not much movement but they add a great pop of color. My only concern with one here would be that they are very docile and you'll be adding it after the clowns--depending on how mature the clowns are, they could really harass the goby (or really any of the others if they are on the more territorial end of the spectrum).