I'll add my 2 cents as well.

I would recommend going to Italy in March. I went this past March, and the crowds that you read about were not there. It also was not too hot, but the weather was quite comfortable. I was there for 2 1/2 weeks and had about half-an-hour of rain. You obviously don't want to go over Easter, but if you go just before then, I think you beat the tourist season.

I flew into Naples since I had a conference in Sorrento and then flew out of Rome. This was cheaper than a direct round-trip ticket, and it also allowed me to see more of the country without backtracking. The trains are very good at getting around, and the drivers are crazy so be wary if you drive. I flew into LHR, and then I changed planes onto BMI into Naples which was a good deal. I was able to book everything on one record, too, even though I was mixing airlines and alliances.

I can't answer your questions about miles or business class too well, but my economy class seat with an empty seat next to me was quite comfortable.