>>51653931AI vs AI is a good way to keep it "fun", because you do NOT want a board unity event to turn competitive. Avoid that at all costs. Hamstring the player options, boil it down as much as you can get away with, and let the AI take the wheel wherever possible. PES and WWE games do this well because the AI in both games is already fucking retarded, and the only "meta" you can engage with is trying to tard-wrangle that AI, only for it to do whatever it wants anyway.
I don't know SF6 well enough to tell you what you should and shouldn't do specifically, but if you want advice, keep enough customization for it to be interesting, but leave out enough that metafags and tryhards can't just run in and style on everyone that doesn't know better.
Also, buckle up. You'll be planning for way longer than you think you will in advance of the event. Be ready to commit at least a month if you want to put on a half-decent show.