We are having a civil ceremony with a magistrate as the officiant. It is being held at the same area where we are having the reception. The officiant is someone who I know (went to school together), but we've never been close friends. More of a "small town, so everyone knows everyone" kind of thing.
So A) what is the etiquette for offering them the option stay for the reception? Send him an invite? Send him an email?
And

paying/tipping. He is not charging for his services, but he is coming to perform the ceremony outside of his normal court hours?