There are 1000 ants on each level, but it could probably handle more without much problem.
Viewing post in Million Ant Moving Company comments
Up to date? Sadly, no. I learned my DOTS in a course on Udemy (here) when it was on sale, but the course was already out of date by the time it launched. It allowed me to learn the underlying fundamentals of it though.
ECS/DOTS has been so troublesome this way. I think it still has a heck of a long way to go before it can replace the simplicity of normal Unity stuff with regards to physics. A simple one line collision check in normal Unity physics can take dozens of lines inside of ECS/DOTS. Procedurally adjusting colliders in DOTS physics is like trying to figure out a cryptic magical incantation, with the current scarcity of examples/documentation. Don't even get me started with scripting triggers in DOTS physics. Unless you really want/need to use it now, I'd recommend waiting a bit longer, at least until they have everything out of preview.