Don’t forget the thousands of mods, too. And like the other reply said about server/game world settings before you start playing, there are mods that add even more settings to tweak, or they make gameplay smoother (or harder), or they add new things like weapons and vehicles. There are even entire new maps to add to play in.

It’s very doable solo, but it’s kind of a slog if you want to do anything significant in a playthrough, plus it can get very lonely and isolating.