wrapping around the Best of the Adriatic -- update

It appears that the Rome-Volterra train will take at least 4-1/2 hours unless you can manage to make the 9:57 AM departure from Termini. There aren't many trains to Volterra, and if you just miss one you'll wait 2 hours for the next. The last one departs at 2:12 PM according to both TrenItalia and the Deutsche Bahn. Given that there doesn't seem to be a great deal of service into Volterra, I'm not sure it's a great place to use as a base for several days, but there may be workable bus options to towns you'd like to see.

There are many good places to visit strung along the rail line between Milan and Venice, including Verona, Vicenza and Padua. That's certainly a great area to spend some pre-trip time. Northern Italy can be cool and wet in April, so be prepared for that.

I don't know Volterra, but between landing in Rome and ending in Venice, you could stay in Bologna. It's a comparatively quiet town (so good for getting over jetlag) and a train hub, so lots of trains from Rome and to Venice, plus easy day trips to Padua, Ferrara, Ravenna and more.

You can get cheap, direct flights between Rome and Dobrovnik. We did the same tour a couple of year ago and opted for the flight. As romantic as an overnight ferry sounds....well, actually that sounds awful to me; hence our flight. :-)

We used GoOpti for a van shuttle service between Verona and Ljubljana at the beginning of our trip. It was very affordable and convenient. They picked us up at our hotel and we stopped a couple times to pick up others and then went straight to Ljubljana. Highly recommend.

If you have only spent three days in Rome, you must spend more time there. I have been to Rome twice, both times for a week and I still didn't see all that I wanted.

You probably have been to the Naples-Pompeii-Sorrento-Capri area as well as Florence and Venice, which are must see places. There are many other places that are worth a day or so. Sienna is a top choice. Ravenna is amazing with its Byzantine era sights. The Tuscan and Umbrian countryside is filled with great paces other than Sienna. Pisa, San Gimignano are others. https://www.viator.com/Florence-tourism/Siena-and-San-Gimignano-Tours/d519-t3335

Assisi and Orvieto are in Umbria and close enough to Rome for day trips or renting a car.

In northern Italy, the beautiful lakes near the Alps are great.

Thanks, everyone, for your replies.
I have been to just about all the suggested alternative places mentioned except Bologna, so I will keep that in mind.
It is a little problematic for me that the 3 places highest on my list (Matera, Rome, and Volterra) are so far from each other. But I do have time and I enjoy trains, so it's doable and pleasant.
I'm open to more ideas ...

Puglia has many interesting destinations. I haven't been to Bari, but I've read that it is nice. I like the baroque city of Lecce, Alberobello (for the trulli), and the many picturesque towns in the surrounding area that I was able to see in 2015. That summer the Lecce tourist office was organizing van trips to a lot of the small towns around Lecce. They weren't really tours; the driver basically dropped us off in each town and pointed in the direction of the cathedral/old town/main sight, and we met back at the vehicle X hours later. This was a great way to get to a lot of small towns without trying to coordinate public-transportation schedules. In the absence of those van trips, I believe it would have been impossible to cover more than 2 of the little towns in one day. As it was, we were able to see four or more. They were quick visits--I often wished for an extra 15 or 30 minutes--but to be able to cover that much ground without a rental car was fabulous.

Ravenna is just a bit out of the way, but I loved it for its beautiful historic core as well as the mosaics.

You are passing up,a pretty good opportunity to look to the East.

SharYn,

There are so many possibilities, it's hard to know where to begin.

In terms of transportation, you could also consider flying into Munich for a few days prior to the tour, as that provides reasonably easy links to Ljubljana. There's a direct rail departure at 12:17, arriving at 18:32 (time 6H:15M) and that will be one of the easiest trips. If you wanted something a bit different, you could also use one of the Van transfer services such as GoOpti, which has departures from Munich, Salzburg and other locations (including a number in Italy).

The main issue I found with the Adriatic tour was getting out of Dubrovnik after the tour ended. Many of the budget airlines only provide seasonal service, so that limits the options. I found that Croatia Airlines was the easiest way to get back to the other side of the water (unfortunately many of their flights have about two stops, so that will be at least a seven hour trip). For me the flight was preferable to using up valuable holiday time on a Ferry.

I'd suggest arriving in Ljubljana a few days prior to start of the tour, so that you can see any sights not covered on the tour. You could also stay in Dubrovnik a few days after the tour for the same reason.

I can well appreciate your change in "travel strategy" after retirement. The year I retired, I took off to Europe for two months, and it was an excellent way to celebrate the occasion!

I really appreciated everyone's suggestions as I planned this trip and wanted to let you know how it is shaking out --
I couldn't easily find a way to include Volterra so I'm flying into Venice instead for 3 nights and will get over jet lag there. (I've been 4 times before, so it will be a good place to relax and just enjoy without needing to see everything.)
Then I'll go to Ljubljana one day early (either train or shuttle) and begin the tour.
At the end of the tour I'll stay 2 extra days in Dubrovnik, then take the overnight ferry to Bari and on to Matera for 4 nights. (So I'm not wasting a day and still get to visit Matera.)
Then I'll get up to Rome for 3 nights, by train or bus.
The biggest change is that a friend is renting an apartment in Paris for 2 1/2 weeks and invited me to join her!!!
So I'll probably fly (maybe take the train ... I do love trains!) to Paris.
Almost everything is booked or awaiting confirmation. I'll be staying in convents in Venice, Matera and Rome, booked through MonasteryStays.com. The locations are good, the rooms are private with own bath, and the prices can't be beat, a necessary plus for a solo traveler like me.
My main flights are on Norwegian Airlines in and out of Oakland. I flew them this past Fall and was very happy with the comfort. (Just don't buy the meal package. They have a snack menu with sandwiches and drinks for much less money if you don't want to bring all your own food along.)
4 weeks has turned into 6 1/2 weeks.
And I can't wait!
SharYn

Boy, your friend must be awesome!