It's great that you're doing so much research - much better than the average uninformed customer that sets up a tank and in 3 weeks has a BTA or LTA in there under fluorescent lights.
Seeing as your tank is only a 20, it will be subject to more fluctuations in water quality, temp, etc... harder to find its groove, stability-wise. I have a 20 with a baby BTA now in there now, and it is more challenging than my other tank, and more work...
My ocellaris clowns did great for almost a year without any anemone - they liked soft corals, and especially LPS (Hammer, Forgspawn, etc). Anemone not necessary, but I'm glad to have got one after almost a year and a half.
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Alan
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