20 gallon fowlr

I have a 20 gallon long tank running for 1 year. It currently has 2 clowns and a yw goby. I have a HOB filter, protein skimmer, and oversized UV light. I would like to add some colorful and practical fish. Here are a few possible additions I came up with, which one do you all think will work...

Hey guys Struggling to stock my tank as everything I like seems to have an aggressive streak! I loved the royal gramma but my friends has beat up his whole tank which is deterring me. The guy at the LFS suggested an Aiptasia eating filefish, does anyone have any experience with these? I have...