Adult content should definitely be allowed, so number 3 is the best.
Also, I'm insanely for the idea of a tagging system and filters by price and content, also open commission status. I have wanted this for years now to make it easy to find open artists who can fit my intended budget for a piece and also draw what I would like. Currently I experience some commission gridlock because searching for open artists on sites like FA is daunting, and more a "I'll have to take the first thing I see" sort of deal.
If we had this implemented, I wouldn't end up commissioning the same two artists all the time because it'd be easier to find new people to fit what I want.
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