You are going to have a fabulous time! I have not done this one but did the 21 day tour. I took a LeSportsac Medium Tote I used for my bus bag. I had snacks, water, guidebooks, kindle, rain jacket/umbrella in there and just left it on the bus. The bus driver will likely have water, wine, beer and since it's a family tour possibly soda for sale. You just put a hash mark by your name on the list at the front of the bus and settle up with him/her at the end.
On bus days the guide will usually do some talking about your next destination. You might have some language lessons or a little bit about history/culture/geography etc. I never minded the bus days. My bus (in 2014) did not have wifi or outlets. You will likely be using the same bus company, Heidebloem, so you may or may not have connectivity. BTW, the bus drivers are uniformly excellent and a real addition to the group!
On our Venice stop I took 2 days worth of clothes and toiletries in my Bus Tote in to Venice and left my suitcase on the bus. Even though I had Rick's convertible backpack I knew I wanted to take as little stuff as I could get away with in to Venice on the vaporetto. The bridges are actually steps not ramps so you have to lift and carry your suitcases if you have rollers. Consider that when you are thinking what day bags you will take with you.
I also recommend a small journal like a moleskine notebook to make daily entries. You will be surprised at how much you forget. Some journal on their iPads but I've not done that yet.
Have a great time! What an adventure!
editing to add: I also recommend if you are trying to pack light to do a test pack soon. Really, it is eye-opening. I would have everyone test pack and have a packing list. Also, I found it easier to stay organized using packing cubes. That way it is easy to reassemble your bag in the AM when you get ready to leave. It's also easier to see if you have forgotten anything as you are not taking everything out of your suitcase. You only have one one-nighter which is good but you are moving every other day otherwise.
