Rome Marriott Park Hotel

We will be based at this Marriott for a conference this July. I do know there is a shuttle service but wonder about other options. 1. What is the cost of a taxi to the hotel from Fiumicino? If we opt for the hotel shuttle, where do you find it? 2. Has anyone taken the Corcco Bus 128 Colonnello Masala stop to the center of Rome from the hotel? Is there other public transportation to consider? 3. What is the cost of an average taxi ride to the city from the hotel? 4. Is the shuttle service plentiful enough that other options are not necessary? I know hotel personnel would have these answers but don't want to wait until we arrive. Thank you,
Jan