but is it possible to give the invitation permission to users with a minimum number of posts, for example users with 50 messages and more?
Take a look at the settings
(General settings->Limit invitations).
You can set the 1st and 3rd input field to 0 and the 2nd to 50. This means you can't send any invitations if you haven't created any posts yet. The number of possible invitations increases every 50 posts by 1.
user1 (0 posts): can't send any invitation
user2 (50 posts): 1 invitation
user3 (736 posts): 15 invitations
With the update to 5.0 did it also become compatible with simple points?
No, it did not (only Advanced Points)
Could you please implement this for one of the next releases?