Alrightly......
We did a VERY similar trip last summer in my Zed and it was amazing. I'm trying to field most of your questions but will forgot some most likely.
Col De Turini - great road, not much around it other than a small village at the base of the road, and a small hotel/cafe at the top. We stayed in Monaco the night before and got up silly early to drive the F1 track a few times, and then head up to the Col De Turini on route to Italy. Some nice little places for breakfast in the little village though.
Monaco - we stayed in the Novotel, it was around £120 for the night with parking, no brekkie. Which was very reasonable, and a very short walk to the Marina (I could look out to the marina from the balcony too!).
In Italy, if you have time I would recommend the Ferrari museum and tour, very cool and reasonably priced. This is in Maranello.
Roads in Italy - Near ish to the Ferarri place is Bologna, Heading off to the south East from there is a road called SP65 - definitely recommend a drive up&down this. Its a biker road and was full of sports bikes when we went.
Lake Garda - Yes!! Lovely place, we stayed for one night on our way up to the Stelvio Pass. The misses liked it so much we are going back there next month. On route to our over night stop we did a full lap of the lake as the views are incredible, and there are loads of tunnel to keep the car happy.
Drop me a PM if you have any questions, as I say, we did near enough the same route recently.
Matt