I was wondering what the typical size is of a homebrew club. They seem quite large.
It varies wildly based on the club. I've been to some club meetings that were <10 people, a great many in the 20-40 range and then there are some clubs like QUAFF or the Falcons (my club) where 70+ is normal on meeting day.
Important thing to remember, no matter what - the people there are beer nutty. You're presumably beer nutty too. You have common ground. Most of us are also socially awkward, so... it's all good.
Easy way to get involved and break the ice - volunteer to help setup or tear down!