Oh - and what about museum passes?? We will be in Rome for 4 whole
days - is it better to purchase individual passes or not?
This subject has seen a lot of discussion lately as there have been some wrenches thrown into tourist passes recently. The tall and short of it is that yes, you definitely are going to want advance, timed-entry tickets for the most visited attractions to avoid long ticket queues or, in some cases, to gain admittance at all. Some of those attractions require advance reservations even if using tourist passes so those do not provide the convenience they once did. So, just off the top of my head:
Colosseum, Rome: advance timed-entry tickets or mandatory reservations (if using the Roma Pass). Tours are also available.
Vatican Museums, Rome: advance, timed-entry tickets or tour HIGHLY recommended.
Galleria Borghese, Rome: advance reservations are mandatory. Not covered by passes.
Uffizi, Florence: advance timed-entry tickets or mandatory reservations if using the Firenzecard.
Accademia, Florence: I'd suggest timed-entry tickets. Reservations are mandatory if using the Firenzecard.
Duomo dome climb, Florence: advance reservations are mandatory even with Firenzecard. If using the card, you cannot make those reservations until you get to Florence and by that time all available slots may be booked.
As you are only going to be in Florence for 1 full day, you are going to have limited sightseeing time so a pass would not be economical, and with now needing to book advance reservation times at the Colosseum, I don't personally recommend the Roma Pass. That one does cover public transit within the historic center (not to/from the airports) but for as little as we used transit, it wouldn't have been all that useful.
Editing to add: should your one full day in Florence be a Monday, be aware of museum closures (Uffizi, Accademia, Palazzo Pitti).