I have the same tank with similar setup; I have a small koralia powehead running with an aquaclear hang on filter running for 2 years now. You do not need a sump or a skimmer.
Although i do not necessarily agree with u on the butterfly or tang selection, i think you are doing a good job so far with your corals. They are nice, easy lps and softies that dont need a skimmer or extra water volume so long as you are good with water changes.
Clowns and different gobies are good choices for this size tank
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