https://en.m.wikipedia.org/wiki/Dunbar%27s_number

I would argue, that communities of dunbars number to may 1'000 or around this could be a good measure for federal communes. So they have the possibility to decide on all local stuff on how to handle it.

Then there still can be a cantonal/district level and a state level.

And I believe, that the Swiss demicracy is very stable and balanced.