There are too many variables in your question for anyone to give you a good answer.
Only trust points can be converted to MRPs. Legacy points and trust points deposited into the exchange cannot be converted to MRPs. TPs expire in 1 year although they generally extend them for a year.
When are you going to Italy, 2017, 2018 or further out? I would not recommend buying a TP now for travel that far out. If you convert to MRPs now be aware that what you can get today might not be what you can get a year or two down the road as Marriott increases individual hotel's category.
Plan your trip before you think about points. You may want to go to places where there are no Marriott hotels. Cinque Terre and the Almalfi Coast are two examples.