Ciao Tony and congrats on your upcoming golden anniversary!
For Tuscany, I'd recommend in Siena or just outside it to the south. Take a
look here - the Villa Corsanello, Podere Cunina, San Giovanni in Poggio are all on the northern edge of Val d'Orcia so closer to Siena than the others, making you a bit more central for all of your day trips. Any of those would be perfect as far as location goes. You can also stay right in Siena, as long as you find a property outside of the city walls with parking so you don't have to worry about driving in to the limited traffic zone.
You can do a week in Tuscany there, then move down into Umbria for your second week (or opposite). Depends on where you fly in to... and that should be the first thing you decide on. Keep in mind that weekly rentals in that period are required and almost always go from Saturday to Saturday so that you can figure out dates.
As far as where to fly into... I'm American but generally fly out of LAX on the west coast, so not sure what are the best routes for Italy are, if you can fly direct. From West coast there is always a layover somewhere. If you can fly direct from Miami to Rome, that would probably be a better deal and shorter flight... but also check flights to Florence. Sometimes, if you have layovers, you might as well fly into Florence and skip Rome. It is what I do now... Lufthansa and AirFrance fly into Florence and the difference in ticket price is alright considering I skip train fare.
Also check car rental rates - maybe cheaper to rent from Florence? There's a search box at the
bottom of this page that checks across various companies, to get you started.
For now, start checking flights to get an idea of the best solution for your dates, and that will give you an idea of how to organize the two weeks.
If you fly into Rome, I'd do Umbria first, but if you fly into Florence, then Tuscany first.
I definitely think you don't need a tour company - having your own means of transportation will let you decide where to head off to each day, or if you want to stay in and relax! Definitely plan some of those types of days in... there is a lot to see (as you can see from our proposed
7 days in Tuscany itinerary) but if you take it slow and are not in a hurry, you will enjoy Italy better! La dolce vita is just slower and needs to be savored, including lots of delicious food and wine
