We have booked a couple tours in Rome through Dark Rome and are planning to do the Murano/Burano tour they offer in Venice. They also have a Doge's Palace one available if that's something you really wanted to do. We are probably going to stick with the included tour for Venice only because none of the additional ones really appealed to us except Murano/Burano and Dark Rome is a lot cheaper than booking through Viking.
I'm kind of leaning towards maybe booking the Murano/Burano tour for Easter Sunday just because I don't know how much else is going to be open. But we may do it Saturday instead and just spend Sunday wandering around and exploring since it will be our last day.
Getting to the airport is also puzzling me. I found what I think is the same transportation service we used for
ABD but it is pretty expensive. It's 110 EUR for up to 4 people, and with everyone going their separate ways after the cruise, I don't know how feasible it's going to be to share something like that. I'm sure there has to be some kind of public transport option but I haven't delved too deeply into other options just yet. I'm still trying to wrap my head around what we are going to do once we get off the ship but before we can check in to our apartment.