Jan-
Oh extra nights are always good! So now you have 10 nights- correct?
I think at this point only you and your husband can figure out how to allot your days.
Make a list of all the things you want to see/do in both Rome and Florence.
Then prioritize. You won’t be able to do/see it all.
Check open/closed days. (Ex- Vatican closed on Sunday, Borghese is closed on Monday- IMO this museum is a must. You are in Rome on a Sunday and Monday).
Don’t overload your days and be very honest about how long things might take.
Your first day in Rome is a jet lag day. Everyone handles jet lag differently- do you know how you will do that day? We need a nap. Others power thru. Either way choose a lower priority venue this day…just in case.
Because of this a 3 night stay in Rome at start means 2.5 days- that .5 day being your jet lag day. So 4 nights at start might work better for you. Rome is a busy hectic place. You might want to escape after just 3 nights. Lots of thing to consider!
I would only schedule one major venue per day- ex- Colosseum/Forum/Palatine will take a really full 2/3 day- (at least they did for us each time we have visited) and it was an exhausting day at that. Don’t add anything more that day than maybe wandering neighborhoods, visiting churches, sitting in a piazza enjoying apertivo.
You will need tickets booked in advance for all the major venues. Is that something YOU want to deal with- getting up in the middle of the night to book Colosseum tix when they become available on Rome time? Or do you want a guided tour- simplifies it a bit- they take care of the tickets. We did a guided tour with Walks of Italy on our first visit and glad we diid, Subsequent visits we’ve gone DIY or used RS guide.
Same for Florence. You could spend a month there and probably still not see every museum. Prioritize. One big museum each day would be plenty for me. There are lots of “smaller” venues just as interesting, historic and important. I can tell you our favorites but your interests might be completely different.
Do you want to try to add a day trip from Florence? Both Siena and Pisa are easily done. I’d give Florence 3 nights if this is your plan- that leaves you 1.5 days actually sightseeing IN Florence and 1 full day for the day trip.
Tuscany- I would probably say since you are getting a car- get the car for as long as you can and get good use of it. So 3 nights there allows you to spend a good amount of time tooling around the countryside. (If you want to wine taste be sure you have a designated driver). But the resort you are staying at has so many activities to choose from you might not care to spend that much time away from the resort.
Whatever you do: slot in time each day for gelato and time each evening for apertivo- just sit and enjoy the ambience in the beautiful piazzas.
If you don't have an Italy Guide yet- you can use these lists as a starting point to choose/prioritize what you'd like to see/do
https://www.ricksteves.com/europe/italy/rome
https://www.ricksteves.com/europe/italy/florence
https://www.ricksteves.com/europe/italy/tuscan-hill-towns
Feel free to post what you come up with as a daily itinerary- maybe start a new thread?