Hello! Welcome to the forum!
I think you might be pushing it with those 3 fish. I have a gramma and it stays in the rockwork ALOT, lol. The clown would be OK with a blenny or goby, there are smaller sized gobies too so you might be able to fit in the 3 fish. Check out liveaquaria.com and look at their nano fish section. Great reference site.
As far as cuc, I would go with a couple hermits, a few snails for algae and a couple snails like nassarius for sand stirring and uneaten food.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.