Actually, it's over 30 now, but 25 was the milestone for me. A quarter of a hundred people!
So I posted the project to Hacker News yesterday and even though the post didn't gain any traction, I'm actually happy about that because it still lead to a lot of people signing up. And right now I wouldn't even know how to "manage" the amount of people a successful HN post would probably bring in.
Also, I searched for a subreddit that fits the Club's theme - just one - and made a post about it on there. Because of the subreddit's size, the post now actually still is at the top.
But the best thing isn't that people signed up, but that some of them started to give their input. That's an amazing feeling I have to say, and probably the real milestone.