Staying overnight in Orvieto is a fine idea, but you also have the possibility of renting a car in Foligno, which is about a 20 minute drive from Montefalco. You also have the possibility of picking up a car in Chiusi, so if you want to see that town, that also might be an option to pick up your rental car there.
Montefalco is a lovely town with beautiful wine but driving around central Umbria is so easy, you can really pick any number of places, and staying in a farm is also a great idea. Be aware that the town of Assisi is jam-packed with visitors.
Days will be getting much longer in June, with the sun not setting until 8pm. Therefore, you can pick up a rental car between 4 and 6pm and still have a lot of daylight for driving to where you are spending the night. What you don't want to do is take a train from Sorrento and arrive someplace when the car rental offices are closed for lunch and you are stuck with your luggage until they re-open.
Many of the hilltowns of Umbria are very steep -- Gubbio and Spello being two of the steepest. Montefalco is also a very steep town. Combining lots of steep hill climbing in a single day can be fatiguing, especially once the weather starts turning very warm (which it most likely will by the second week in June).
Most everything in Umbria closes from 1pm to 4pm. Therefore, when you are planning day trips, put the American clock aside and try to plan things with the Italian clock in mind. Italy does not have a 9-5 "day", and many people make the mistake of starting out a 9am to "day trip" to distant towns only to find them starting to close down by the time they have arrived and found parking, and climbed up the hill to see them -- and it can be rather boring.
Instead of getting in the car in the morning and driving to your most distant target hilltown, planning to see another on the way back, consider going to the near one first thing in the morning, then driving on to the second in time for a 1.30 lunch. That way, you'll be enjoying the second hilltown when it is starting to come back to life and everything will be open until 7.30.
While it is true that on your first day of driving, it is good to arrive at your b&b or hotel before dark so it is easier to find, once you are there and doing day trips, you will find it fairly easy to drive at night in Umbria. I wouldn't make myself the prisoner of doing day trips in a 9-5 framework so you are leaving interesting places every afternoon just as towns you wanted to visit are being enjoyed by the locals.
However, if you decide to stay at a farm (a wonderful idea), it is best to pick one that also has a restaurant attached so you can enjoy wine without needing to drive after.