Quick update on @White Noise scaling.

It seems the current limit is ~ 50 members in a group. Inviting additional members fails to deliver invite welcome messages to the new user.
So best keep your groups under this size for now.

We didn't focus on scaling at all so far.
Step 1 was to make it work.
Now comes a lot of performance improvements, which should also help with scaling.

I'd love to reach at least 10k members in a group, in theory we can do even more, but thats hard engineering ahead.