According to some data I collected, you can make ~2300 bells/min diving, which means 500k would take a little less than 4 hours.
There is research showing that adding lanes only helps for maybe six months. Then people realize that the route is better and change the routes they take, which leads to more congestion again. Fewer lanes can actually decrease congestion.
https://smv.org/learn/blog/how-does-roadway-expansion-cause-more-traffic/
This post covers it pretty well https://phauer.com/2015/checked-exceptions-are-evil/
I think there is a strong argument that we have been post human since we developed writing and that a 'person' encompasses more than just their meat sack. I was first introduced to this idea by the book Natural Born Cyborgs. You are taking a narrower view of the word evolution, but I'm not totally sure it's justified.
Darmok and Jalad at Tanagra
I think your server will only download content if one of your users views/subscribes to it, so maybe you could disable signups so that you're the only user on your server? This would still allow users on other servers to subscribe to your communities.