Welcome!
I assume CK2 is Crusader Kings 2? If so, it already has a Linux native build. For Guild Wars 2, you can download it from Steam and use you own credentials on the launcher and play like that. It would be easier that way.
For different distros, it doesn't actually matter that much. Just pick one you like and delve into it. You may want to change it when you learn more about Linux, but that's for some time later.