That inches per gallon rule just doesn't work very well for marine tanks. It really depends on the fish. I agree that the angel, clown and neon goby should be just fine as long as you're not planning to add those in addition to what you already have. Also, give a lot of thought to the type of clown you pick. The more aggressive species (Maroons, Clarkiis, Tomatos, etc.) will pretty much consider the whole tank their territory, and may end up harrassing your other fish. Perculas, Ocellaris and Skunk clownfish would probably be good choices, though.
Everyone's going to have different opinions as to how much is too much, though. In my 46g, I considered 1 Maroon Clownfish, 1 Smith's Blenny and a Mystery Wrasse to be plenty.