The Lost Cities Keeper Wiki currently has a very active forum.
Yup, that is an example of a wiki where Discussions is going to take some getting used to... it will suck. Forum has 4 different ways to sort threads and Discussions has 2 and one of the 2 is a complete mystery on what the algorithm is ("Hot").
Yep.
If you are looking to create "forums" on a UCP wiki, you have to create a new discussions section. That's the closest thing to a forum. Or you can use a message wall.