I have one world/save file since I bought the game in 2014. I play with aging off but I still have plenty of room to play out my ideas (2000 hours played). If I have a new idea, goal, or challenge I ...
Probably have somewhere in the 20 to 30 range, but there are about 7 that I actually care about and have played beyond one or two sessions. And about 3 that I have played for a long time.