Bosnia-Croatia-Slovenia

Rather than add more places, I'd suggest that you change some of your one night stops to two nights.

I would add the nights to Slovenia and allocate one full day to visit Ljubljana. Can be easily done from Lake Bled as a base.
I am assuming that you will have a car?

Yes we will have a car and will add a night or 2 in Slovenia so we can take day trips in the area.

This is a very ambitious driving trip! Google Maps shows nearly 22 hours of driving time--a total of 3 days driving time out of 12 days.

Zagreb ---> Sarajevo (5 hours);
Sarajevo--->Mostar (2 hours);
Mostar--->Dubrovnik (2 hours);
Dubrovnik--->Split (3 hours);
Split--->Plitvice Lakes (3.5 hours);
Plitvice--->Postojna (1 hour);
Postojna--->Lake Bled (3.5 hours);
Lake Bled--->Zagreb (2 hours).

That doesn't include stops for lunch, toll stops, parking, locating hotel, etc.

We did a similar trip but had 3 weeks and flew from Zagreb to Split (with a couple of nights in Mostar from Split.) Then we worked our way up the coast. For a more relaxed trip, try for more 2-3 night stays.

One option would be to visit Zagreb, Sarajevo, Mostar, Dubrovnik and Split--then fly back to Zagreb from Split. Pick up rental car in Zagreb and drop off in Split. Look at Croatian Airlines for low-cost flights between Zagreb and Split.

We are doing a very similar trip this summer. But we have a few less 1-night stays than you do. The biggest difference is our time in Slovenia. Ljublana is very central and 2 hours or less from the other destinations in Slovenia we want to see (Julian Alps, Lake Bled, Postojna Caves and Predjama Castle). A Slovenian recommended to us that we use Ljublana as our central home-base while in Slovenia to cut down on the need to change hotels. So we'll be spending 3 nights in Ljublana, 1 night in Zagreb, 1 night in Mostar (stop in Sarajevo on the way), 3 nights in Dubrovnik, 1 night in Korcula, and then parse out the remaining nights get from Korcula back up to Slovenia.

After Korcula, we may do 1 night in Zadar, then go to Piran the next day with a stop on the way up for a few hours at Plitvice. We are thinking not to waste a night in Plitvice since Rick's book makes it sound like while the waterfalls are beautiful to visit, they can be seen in a few hours and the area itself isn't much of an interesting place to stay.

We will only have 3 days of 5 - 7 hour driving, and those drives all involve stops along the way we are looking forward to (i.e. stopping at Sarajevo on the way to Mostar or stopping at Plitvice on the way to Piran). The rest of our days of driving will be 2 hours or less.

Happy planning!!

There has been alot of great input and I appreciate it. I think that we will modify to the following with a void that I need to figure out but should not be too big of a deal.
Zagreb - 1 night
Sarajevo - 1 night
Mostar - 1 night
Dubrovnik - 3 nights
Split - 2 nights (sightsee in the area a bit)
Some coastal town on south side of Istrian Peninsula - 1 night (see Plitvice Lakes, not really on the way of course)
Postojna region - 3-4 nights (use as base camp for castles, caves, Lake Bled and possibly Venice to see DaVinci exhibit)
Advice here needed possibly stay a night in Venice to make that visit easier and less rushed, not sure it this is necessary if you can get there in 2 hrs from where we are staying above.
Zagreb - 1 night and fly out

Sorry to sound anti-Da Vinci, but similar exhibits have been traveling around Europe and the USA for years, so I wouldn't make that the basis of a special trip. I'd make this trip about the countries listed, where you're already spoilt for choices of destination, and not cross into Italy.

I agree with above poster about skipping Venice; however, if you really want to go to Venice, you might see if the ferries from the Istrian peninsula to Venice are running and do it as a day trip by ferry (leave the car in Croatia for the day). For example, there is a ferry from Rovinj; you could stay there a few days, making the day trip on one of those days.

You've got 3 one-nighters in a row at the beginning of your trip when you are probably still recovering from jet lag. I find one-nighters to be tough as you really only get a half day or so in each of the cities once you take into account travel time.

Also, make sure that your rental agreement allows you to take the car into Bosnia.

Wow I am so glad I posted to this forum. I have some other things to check into. We are doing this end of sept and first of October which is about when ferries either stop service or start limiting it.
I will eliminate Venice.

We are doing a very similar itinerary and are thinking of cutting out a night in Zagreb so that we can stay the night in Sarajevo (prior to a night in Mostar followed by 3 nights in Dubrovnik). Have you found any good-looking spots to stay in Sarajevo other than what RS lists in his book?

Yeah we are going through Bosnia because my grandmother was from a city between Zagreb and Sarajevo. That is probably a tid bit I should have added in my initial posting. It better supports our crazy drive the day after we arrive.

As for accomodations, I starting looking at TripAdvisor, and after not being able to put a deposit on a stay in Dubrovnik I came across booking.com from which I could reserve a room. Then from that site I searched into Sarajevo and Mostar. I was just looking for a place that was central, seemed to be a small family type place that still offered parking. Of course good ratings was important.

If you're still looking for a hotel in Mostar, Villa Fortuna worked well for us. They do have parking and are centrally located.

Okay if anyone is still reading this I have modified the trip a little and wondering if we should eliminate a couple things
14 nights total is all we have

Zagreg - 1 night
Sarajevo - 1 night
Mostar - 1 night
Dubrovnik - 3 mights
Split - (1 or 2 nights)
Plitivice Lakes - 1 night (we have hiked Alaska and the cascades etc...so if we skip this will be missing something big?, or keep this and go to 1 night in Split)
Pazin - 3 nights (or some other central location in the region, trying to go truffle hunting and will day trip to Pula/Rovinj maybe)
Bled - 1-2 nights (depends on Split and Plitvice Lakes if we can stay 2 nights)
Zagreb - 1 night

As I've mentioned before, we have a similar itinerary to you. When planning our route, we had a few extra days to spend in the northern part of our trip. I posed the question on the forum a couple of months ago of whether we should spend time in Istria or focus on Slovenia. I posted it in the Croatia forum and folks recommended to spend time in Slovenia over Istria. https://community.ricksteves.com/travel-forum/croatia/istria Since you only have 1 night in Lake Bled, you might want to think about adding your 2 nights from Istria to Slovenia. Then again, I'm only going off the recommendations of others at this point, as we have not yet to taken our trip!

Here's one option to consider--fly from Zagreb to Sarajevo the day you arrive--check Croatian Airlines for flights. Add the first Zagreb night to Sarajevo. That would eliminate 3 one-night stays in a row. You're going to be exhausted by the time you get to Dubrovnik! Do a short-term car rental if you need it to visit your family home.

Then bus or train to Mostar. Bus or train to Dubrovnik. Pick up your rental car when you leave Dubrovnik.

Skip Plitvice for 2 nights in Split. Plitvice is nice but if you're pressed for time, I'd skip it this trip.

If you skip Istria this trip spend time in Ljubljana/Lake Bled. If you go to Pazin then maybe skip Lake Bled. We didn't go to Pazin so I'm not sure what's there. Then, one or two nights in Zagreb at the end.

Based on our experience, I'd skip Istria to spend time in Ljubljana/Lake Bled but that just one opinion.

Something like:
Sarajevo - 2 nights;
Mostar-1 night;
Dubrovnik-3 nights;
Split-2 nights;
Pazin-2 nights;
Ljubljana/Lake Bled-2 nights;
Zagreb-2 nights.

There are so many options--I'd just be cautious about trying to cover too many miles in 14 days!