being an avid non-lover of hentai... I would say this is a much better idea and I would do it... free costume and con fee, who wouldnt'?
I think the your idea for a club/cafe with anime stuff was the best because there really isn't a good one in portland. There is backspace, but theres nothing to do at backspace really, so it kinda sucks. It'd be cool if you made another hangout/cafe place like backspace. But then you got like a little theater set up and always had the newest episode of every unlicensed series downloaded or bought if it's licensed, so then people could just go down there every week and watch the newest ep. I know if a place did that, i'd definanelty be there every week to watch the newest episode of whatever series I was keeping up with. But just charge for drinks, not for watching stuff, so it stays real casual. Then also host video game tournaments with small prizes weekly.