Hi Martin and Paulus,
Thank you for all the effort running this great meetup!
It would certainly be instructive to keep stats on how many people RSVP vs actually show up. Do we already keep a percentage of no-shows in mind when setting the quota? It would be a shame to turn people away because it's "full" when in fact it isn't.
If you look at the Ruby user group, they've gotten quite big as well. You can RSVP on their website, but it's optional and not limited. Occasionally it's gotten a bit crowded, but usually growth is quite organic, so the best prediction is really to be able to look back at the last couple of months, and look for venues accordingly.
I think it's a great idea to provide a space for beginners, but doing it during the meetup would be missing an opportunity in my opinion. Again comparing to what the Ruby group does, they went through a similar process, with especially Rails Girls introducing more and more newcomers to the community. The response there has been to try to schedule at least one beginner-friendly talk at each event. That way everyone can just mingle, and new arrivals can make friends with people that have been around for a while. This has worked really well, and it really encourages people to become active in the community.
I'm sorry I can't offer concrete ideas for spaces... I'll keep an eye out :)
Arne