Northern Italy Itinerary Advice

Your trip works. I wouldn't add Lake Como, since it's out of your way. but you could add Lake Garda, since it's very close to Verona (30min).
Sunday am you go to VR from VE by train (1hr trip). If you leave early enough, the rest of the day is actually more than enough to see all of VR. The next morning (Monday) you can check out, rent a car and head to Lake Garda. First visit Sirmione, just 40 min from VR, then after lunch drive to along the western shore to Limone. Spend at least one night in Limone or somewhere in the north lake ( Limone, Riva or Malcesine). Then proceed to the Val Gardena (Ortisei or Selva) in the Dolomites for 2 nights. From the north lake to Ortisei in Val Gardena is less than 2 hr drive. During your time in Ortisei, you can drive to the Pordoi pass or Sella pass or do a full all day loop or you can hike.
Then, when you're done also with the mountains, you can drive down to Siena from the Dolomites (5+ hours plus pit stops).
In Siena, when choosing accommodations, consider that the historical center is verboten to cars. So you either choose a hotel outside the ancient city walls or you must park your car away from the hotel in one of the pay parking lots outside of the historical center, such as Stadium/Fortezza or at the Fontebranda district (€20/day or €2/hr).
Wine is produced everywhere you are along your itinerary. There are very few places in Italy where you are not within sight of vineyards. In your case, the only place where you may not see vineyards is at the very top of the Dolomites (however there are plenty of cellars in Val Gardena).

Val Gardena will be very quiet in October. Many of the hotels close for a break at the end of September.