(1) There are probably people who won't decide to go until it's set with a date, a time, a place, and a price.
(2) There are probably people who've said "I would have gone if it were here" who wouldn't have gone anyway.
(3) There are probably people who've said "Great! It's here, I'm going" who won't show up.
(4) There are probably people who haven't said anything at all, who won't say anything, who will show up anyway and then complain about the lack of work that others put into it because it looked like not many were showing up.
This is the nature of all convention-type events, everywhere, no matter what, unless you insist on paid pre-registration. You guess at the number of attendees to determine the size of the place, but don't expect an accurate count from people's responses. And you'll drive yourself crazy if you start trying to rate how serious the responses are in the first place. The steps that have been taken so far are great. Don't get discouraged. Just keep plodding ahead, set your expectations low for something that's just for fun, and even if only a handful of people show up and enjoy it, it will still build interest and momentum for a next time.