Venice - Riva del Garda/??? - Cinque Terre - Rome

Why not scratch Cinque Terre (it's out of the way) and replace with Florence instead, especially if you are interested in art and culture?

If you're already in Venice, I'd say stick around for a few days to soak it up. There's no place like it.

If Cinque Terre is your other high priority, you could stop off in Verona and/or Parma en route from Venice. You can't go wrong with scenic beauty in that region.

You're flying home from Rome, I take it? If not, you could just stay in the north and plan another trip to see Rome some other time. You know what they say about Rome: a lifetime isn't enough (to see it all)!

I don't see the need to go to the Cinque Terre in November.
I would devote more time to the cities, which offer more to see in Autumn/Winter type of weather.
Venice: 2 nights (9, 10 Nov)
Riva: 2 nights (11, 12 Nov). Not sure how many nights you need there, not knowing what time the marathon starts and ends. If it's starts early morning, you need to be there the night of 11 Nov. If it doesn't start that early, you might consider staying overnight in Verona, about 1 hr away by bus.
You have 6 nights available until 19 Nov, when you intend to spend in Rome.
I would spend most of them in Florence, and use it as base for other places in Tuscany. You could even visit the Cinque Terre from Florence on a day trip, if you absolutely must.