Hi there, Laurie Ann. I'm late to the party here too but a couple of comments?
Renting city apartments versus booking hotels: I'll always vote for first-timers abroad to go with hotels. There are enough learning curves to getting acclimated in a foreign country to begin with that 24/7 desk service can be reassuring, especially if some unexpected event - say a medical emergency - makes having help at hand well worth the choice. Prior to COVID, a great many hotels also included breakfast of some sort or another in the tariffs; another plus in our book. Once acclimated to how Italy 'works" and/or are comfortable that you could handle a fairly large problem by yourself, then apartments can make sense, as in our Jay's case. As someone already said, do you really want to spend time shopping, cooking and washing dishes?
Jay can laugh as he knows that I am only marginally acquainted with my own kitchen. HA!
Speaking of medical stuff, make sure to check your policy to see what it covers, or not, out of the country. Many of us buy at least medivac insurance should we need to be airlifted back to the U.S with support as that is REALLY expensive.
As well - as this is definitely NOT a criticism as it's easy to be seduced by gorgeous photos!!! - I'm sensing that you two could benefit from choices that will make acclimation easier and your trip more enjoyable. You DO have plenty of time yet for lots of research but, well, just your DH's perception that Lake Como will be populated with lots of wealthy people "having fun" .... I'm with some of the others who wouldn't personally choose that area to visit in March; a lot of restaurants, hotels and whatnot there will still be closed for winter.
We've done Rome right off the plane without any issues but I'll agree that it's definitely not a city to be rushed. Yes, it's busy but the historic center isn't all THAT vast, and there are interesting corners for finding breathing room IF you give it enough time to wander away from the most-visited attractions. Florence's historic center is pretty compact but packs a punch; LOTS to see. We've personally no interest in rural stays as we enjoy the sorts of attractions cities and towns offer, aren't interested in amenities such as pools, cooking classes, on-site restaurants, spas, livestock, etc. and like having public transit close at hand for flexibility. Still, I do understand that they appeal to a lot of folks, and it's your trip so go for it if that's your thing. Still, heed the great advice to read up on the rules and regs of driving in Italy, and understand that you won't be wheeling right into some of those small Tuscan towns that have restricted driving/parking zones.
Airports: yes, Venice has an international airport. While Milan has several airports, the main one for most long-haul flights is quite some distance outside of the city, technically in Malpensa, about an hour outside of central Milan. One note about Venice (Marco Polo) is that flights to the U.S. do tend to leave early in the morning and that can create some interesting/expensive challenges getting there via public transit depending on where your accommodation is. The advice is usually to fly IN to that one and out of Rome (Fiumicino) if those both cities are on the itinerary.
If cutting Como and Venice, you could look at little Pisa International (Galileo Galilei) to access Tuscany.