On a similar note, I read that a party needs at least seven people for it to feel like a party since that's when people start standing, forming groups and what happens becomes more dynamic.

I witnessed this myself on a party. A couple were the last for us to be seven, and because they were late, we already started with food and drinks so some went with them into the kitchen to show them some stuff. That's when there were always people in the kitchen for the rest of the night.