Well, Whatever floats your boat.
Upgrading within the 7.x series is a simple process. And if it fails could be undone if you make backups. In just a few moments time. Well at least until the new 7.6 version comes out.
As far as the signature goes the message is not the default message that you posted but that can be changed in the language files. So maybe you did change it from the default. So you could edit the language file again and state a note in the profile page that "no signatures are saved until x number of posts".
For elevating groups based on posts.
Newbies would be null or 0
Users would be say 10
So a new registrant would be in the newbies group. Since they have no posts.
Once they exceed more than 10 posts they would be elevated to the user group.
And so on and so on if you build your groups that way.
So you could tier more features available to the user based on number of posts.
