Itinerary

All three of your options sound great to me. I would like to see you with at least three days in each place (ideally more), but it should give you a solid overview.

You could always do a loop from Milan - Milan to the Cinque Terre, then to Florence, then to Venice, then back to Milan... or of course loop it the other way around.

I would just suggest avoiding Florence on a Monday as most of the major tourist sites are closed.

Torino to the CT (say Vernazza) is about 4 hrs by train. CT to Florence is about 3 hrs. Florence to Venice is about 3 hrs. These are station to station times only. You have 7 days not including your travel days. Figure every time you relocate consumes more than half a day, with train time, getting to the hotel, unpacking, etc. You've already noticed that Torino is not located to make your itinerary efficient, being so far to the west. This is just me, everyone has her/his own preference for # of days. I'd consider doing Torino to Florence to Venice, then back to Milan (assume you're flying out of Milan?), dropping the CT. Substitute a day trip from Florence to Siena for the CT. If you do the CT, make that your shortest stay. If you're flying out of Milan, you have to get back there from wherever your last stop is. Venice to Milan is another 3 hours, then another hour or two to get from Milan train station to Milan Malpensa airport, which is 30 miles outside Milan city center. Every relocation in Italy seems to take longer than one thinks.

I agree with you that more than three places will seem rushed. But you need to count Torino as one of the three.

I'm with Kent, Torino - Firenze - Venezia then back to Milano for the flight out.

If it were me I'd arrive in Milano the night before the flight, just to make sure to get there.