No real hard or fast rule here, but if you've more than, lets say, 75 hours in EU4, I'll give you the side eye if you pick em. They're quite powerful, so available to newer players only.
If the AI attacks another player in his absence, they can demand up to 50% war score, but no more.
So if you're new and interested, please feel free to sign up too! Once we have a list of players, we can get to picking nations and start gaming! The base game is currently 80% off, and multiplayer games use whatever DLC the host has, so you could buy just the base game and enjoy all the DLC the host has bought. Please post in this thread if you would be interested in joining in. We want players for another session of the finest map painter around, Europa Universalis IV, now that the Emperor DLC has finally launched.