We are scheduled next year for a RS tour that starts in Venice. We are interested in traveling to Milan for the tours of the Inter Milan Soccer Stadium, San Siri, and La Scala opera house. Not necessarily on the same day but possible. We will probably go to Italy several days earlier to assure we are on time for the tour and to acclimate ourselves. Any recommendations on how we should handle accommodations and itinerary? Should we book additional days at the Venice hotel that is on our itinerary and ride the train to Milan or should we fly into Milan and then train it to Venice later?
should we fly into Milan and then train it to Venice later
Yes, this would be my choice.
"Commuting" to/from is 5+ hrs of train ride each day ( plus the time getting to/from the train station at each end)
Definitely fly into Milan and spend two nights there (unless you decide on more). You'll only need a one-way rail ticket to Venice, and I bet it saves you some money on airfare, too.
Any recommendations
While Chatting with Inter and Milan fans, I wouldn't dare to call Inter, "Inter Milan". Just... don't.
Second best advice has already being given: stay in Milan a couple of days, then go to Venice.
In Milan, I'd pick an hotel close to the Porta Genova metro station on line #2 (the Green line). This way you'd be at a walking distance from the Navigli neighbourhood, 3 metro stops away from Cadorna Station (where airport trains from MXP arrive) and 8 metro stops away from Centrale Station. Both Trenitalia's and Italotreno's high speed trains depart to Venice from Centrale.
I urge you to allow enough time to walk around and take in Milano Centrale train station. The architecture is stunning. It is in the top 10 of the most beautiful stations in the world.