Are you planning on travelling internationally soon? Does your future wife have a passport? Book under maiden name unless you are in a real hurry to waste some money on a new passport.

FF account changes are done when you mail the copy of the marriage certificate in. My wife traveled only on her passport until it expired and when she renewed with her married name also changed her FF accounts at that time. Carrying a copy of marriage certificate is a good idea though and usually solves any issues.