I would create a User model - limit to 1 record, and set a condition where the UserID = running userID. Select UserID and ManagerId (and Full name) in this model. This gets both pieces of info about the user creating the record.
Then either on your action button or your model condition (like Raymond suggested above), set the fields using a “Field from another model” action. make sure your User model is above your new record creation model in the order of models on the page.
I also wouldn’t set the CreatedBy. I don’t think SF lets you change that.
