> TLDR: One only really needs a community of about 150-250 non-interchangeable like-minded people to be happy and have dating/marriage prospects. In a city of 10K people you can also change your Dunbar community several times if you want to.

While true, this also forces you to change the things yo do to fit the community. If you have, say, two relatively unique pasttimes, you'll be able to find communities for both in most major cities, but will be one of only a handful (or the only!) person who does the thing in a town of 10000.