Base for 4 nights in Hill Towns

That’s a lot of ground to cover in just 3.5 days
You might want to check your drive times.
2 bases might work better but honestly I’d say you need way more time for those 4 locations

Siena probably best bet.

Where are you getting car? Where are you dropping car?

You are looking at 1.5-2 hours minimum between each location not to mention parking issues.

A good tool for initial research is www.rome2rio.com
Will give you an idea of drive time but just know it always takes longer.

My rule of thumb for day trips is no more than 1 hour give or take a few minutes. Add time for looking for parking then actually getting INTO the town, as you will be parking outside the walls/bottom of hill, etc.

Florence is not a town, it’s a large city that deserves more than a few hours. 3 nights ( 2.5 days is usually recommended)

Siena should get a full day as should Orvieto and Assisi.

Agree with Christine. It's a lot for so little time. Florence itself will take more than a few hours.

Rental car for 4 -- is that 4 adults with luggage? It will need to be a fairly large vehicle if so. Not the easiest to maneuver on country/mountain roads or to park. So just be aware of that.

Second, the locations you list are pretty far apart. Orvieto is halfway to Rome from Florence, and Assisi is off to the east. As others pointed out, you'd be spending most of your time in the car if you wanted to visit Florence plus the three towns in 4 nights (5 days). I suppose Arezzo would work as a rather central location if you're determined to avoid changing hotels for 4 nights and driving to your destinations as day trips.

Do you have flexibility to add a couple more days, or to adjust your itinerary to hill towns closer to each other?

4 nights is not 5 days

Welcome to the forum! I also saw your other post. We can give you better advice if we have more information. When is your trip? What is the total number of days? Where will you be flying into/out of? Have you made reservations? Have you reserved your car? Have you been to Italy before? Can you drive a manual transmission?

As has been mentioned, that's a lot of traveling and it would be hard to find a good base for everywhere you've listed, considering the time you have. For instance, it's a 2 hour drive from Assisi to Florence.

On our last trip to Italy, we stayed in an agriturismo just outside Greve, which is 22km south of Florence. It worked well and we did visit Siena and several hill towns in Tuscany, all less than an hour away from home base. We were there 7 days. We considered visiting Assisi, but there were closer towns we wanted to see and felt it was a longer drive than we wanted to take.

Also, as someone pointed out, 4 nights is actually 3 days. I think that's not enough time to see everything you've listed.

You list two towns/ cities in Tuscany and two in Umbria. Choose one of those provinces to tour on this trip. You will return!

Siena can, just barely, be seen in a day. Florence cannot. I would stay outside a town to facilitate easy entry, exit, and parking each day. We chose a small luxury resort near Sinalunga, but others love the idea of an Agriturismo. You must give the month of travel when you are talking about a crowded, popular, hot location. By hot, I mean even people who don't care much for pools (like me) relish the jump in after a sweltering day of touring. We also chose a luxury spot to get high-powered air conditioning.

I agree with previous post, Greve or somewhere outside of town. Most of these little towns have areas where you can't drive so you end up parking outside the town and walking up.
We just stayed in Siena but driving in there is very difficult. We did love our hotel, but pricey, The Grand Hotel.

Do the olive oil tasting located between Florence and Siena, can't remember name.
Make reservations at vineyards. We dropped in but it's not advisable.
We did 2 nights Siena, 1 night Assisi. Needed more time. So maybe not worth making it to Assisi which is off to the east a bit (I think 2 hours east of Montepulicano).