I’ve looked around a little, and found some mentions of using Lutris, or running it through Steam (tbh I don’t know how that would work), but I’m not really able to find any guide that explains the process well enough. I’m so used to the game being handled by Blizzard’s Battle.net launcher, so I can’t really wrap my head around how that would work.
It’s your choice, and you can also allow other people to connect to it. The standard settings gives an experience that is close to the real game (as of WotLK), but you can tweak these settings to level faster or whatever you want. Depending on the implementation you go with, there are different ways to add new content - one of them (Azerothcore) is for instance very addon based and you can add bots or difficulty scaling to make things soloable for instance.