Hello brian.westbye, and welcome to the boards,
With the exception of Fano this sounds like many first trips to Italy - Venice, Florence, Rome are called the "big 3" for a reason. Fly into Venice and out of Rome and train everywhere in between.
I would recommend two weeks for a trip like this - depending on how long you intend to visit family in Fano. Add an extra night in your landing city because you'll effectively lose at least part of a day to jetlag and culture shock - I'd say 4, 5, 5 nights with 14 days and then add nights for Fano. If you can spend more time that's great but I'd start on a schedule in this range and adjust.
Fano is on the eastern coast so you could do Venice > Fano > Florence and not back track through Florence but it's a difference of a few hours on the train so it's not crucial.
List what you want to see in each city, decide what you have time for and book tickets for must see things once you have dates. Siena is a great break from the big cities and can be easily visited by bus or train. Pompeii is a really long day trip from Rome so I would consider Ostia Antica for an easy day trip (less than an hour) out of the city with at least some of that 'lost city' experience instead.
Sounds like you're on track, keep planning and have a great trip,
=Tod