Hi Cherry!
I took this tour last year. The itinerary was a little different (I think starting in Venice is so much better!). To help me remember, I'm going in the old order from 2024. My tour also stayed in Lecco instead of Varenna and Bolzano instead of Castelrotto. I travel with a carry-on sized rolling bag and a personal item backpack for reference. Keep in mind that RS hotels may not have elevators, so if you are not as comfortable carrying a rolling bag up flights of stairs, that might be a pro in favor of a backpack!
Lecco - bus pick-up across the street from the hotel, no issues with rolling bags (elevator in hotel)
We did visit Varenna on our free day. If your tour is staying there, I'm not sure how close the bus could get to the hotel and rolling bags might be tricky on uneven pavement/with crowds.
Bolzano - bus drop-off/pick-up across Piazza Walther, no issues with rolling bags but we definitely made a racket! (elevator in hotel)
We didn't visit Castelrotto, so I can't speak to what it would be like there.
Venice - our guide hired water taxis to pick us up at the bus depot, it was a couple "blocks" from the canal to the hotel but nothing too bad for a rolling bag (no elevator, I was on the 5th or 6th floor)
Florence - the bus had to park several blocks from the hotel, it was a walk and there was some uneven pavement, but it wasn't too much of an issue with a rolling bag (no elevator, several stairs up to hotel level then some stairs within to get to certain rooms)
Monterosso al Mare - our guide/the hotels sent vans to pick us up/drop us off where we had to leave the bus (we were split between 2 hotels, I was in the one not on the beach, there were stairs to get to the hotel from town but the hotel had an elevator, but it wasn't an issue with luggage)
Siena - bus drop-off/pick-up near the hotel, no issues (no elevator)
Orvieto - I don't think tours will be staying at the resort where my group stayed, but the resort was pretty spread out along a hill. Some were near the bus (parked at the top of the hill), but others had a much longer walk.
Rome - bus parked several blocks from the hotel, only a few issues with uneven pavement (no elevator)