First time Croatia this September

Sounds like you are planning to visit Slovenia as well as Lake Bled is on your list.

Is there a reason why you are not considering a rental car? It will be so much easier.

I would suggest flying from Venice to Dubrovnik or Zagreb and renting a car and skipping Slovenia. Fly back home from either Dubrovnik or Zagreb - wherever you end up.

A lot depends on how much time you have for Croatia etc.

Thanks for the link scynthia. I will look into it. Thanks for the suggestions Emily. We have never driven in Europe for our previous trips as we just public transportation.
We will most likely do open jaw. Either fly into Venice and out of Croatia or vice versus.

Check Venezialines for ferries from Venice to Rovinj or Pula.
Much depends on how much time you have. It is doable without a car but slightly more tricky.

You will find driving in Slovenia and Croatia very easy. You will lose a lot of time using public transportation in these countries. Seriously. It is mainly buses as well.

This summer we are taking a ferry from Venice to Rovinj (also goes to Pula) - once a day in each direction I think (might be twice a day on some days during the summer). I booked through this site - https://www.directferries.com/venice_pula_ferry.htm I did a fair amount of research and it looks like it gets good reviews.

Re car vs public transportation. Since we have to drive everywhere at home we prefer public transportation in Europe ( it's also way better than in the US). However, some areas it really makes things much easier. After extensive research we decided to rent a car for Istria (Rovinj, etc.) down to Pllitvice back to the coast. On previous trips (Dubrovnik to Split, Slovenia) we did just public transportation and it was OK (in Croatia it was all ferries, in Slovenia I did do some train/bus).

I haven’t driven a car for the 12 years I’ve lived in Vienna. I am a huge proponent of public transportation, but some parts of Europe are just not there yet with their public transportation. Slovenia and Croatia are examples of this. When we go to Croatia and Slovenia (which is very often) we always rent a car (my husband drives). Such a better way to explore those countries.

Thanks. I guess it explains why the Croatia tours are easily sold out as there are folks like me that would rather not drive there. We have checked into gate 1 Croatia tours and most tours were sold out.

Public transportation really doesn't fit to well with a time-compressed itinerary in that part of the world. If you're not in a rush, you can make it work, but you will certainly be able to cover a lot more ground with a car. I had to spend a couple of extra days in Istria in order to see some of the interior via a once-a-week bus tour. It allowed me to see Groznjan and Motovun, as well as other places, in a single day.

It's not clear how much time you have, but your plan right now lacks focus (and includes more areas/countries than solely Croatia). Croatia has a very long coastline and trying to cover both the north and southernmost parts is quite an undertaking. You'd be better off if you constrained yourself to one region where you can reasonably get around easily and aren't always on the go, instead of picking sites that are all relatively far from one another. I had no problem covering the area of Split to Dubrovnik plus a bit of Bosnia and Montenegro using buses (that did mean making choices though, including cutting out Plitvice Lakes and not going north of Split - but, in the end, it was totally manageable in 12 days or so). There is a lot to do in any region in Croatia, so just pick one that makes most sense depending on where you're coming from (or want to fly into/out of). There is ample bus service between Split and Dubrovnik, and Split is a great base for seeing any of the islands. I personally did not find any problems with using public transport where I was.

In croatia,we are looking at visiting Dubrovnik, Montenegro, Bled and
Plitvice lakes.

I will assume, that like me, sometimes you type faster than your mind organizes and you do know that Montenegro is not a destination in Croatia.

If you fly open jaw, arriving in Venice, then the end point of your trip, with out any back tracking will be Podgorica. See what options that offers. Last trip we flew Delta and changed in Rome. The tickets might be a bit cheaper.

You really only need it for certain parts. As I said, we did Dubrovnik to Split (including Korcula and Trogir) completely by public transportation and this summer we will be in Croatia for 14 days and only have a car for 4 of them. I spent a week in Slovenia with no car. So if you really don't want to drive just skip Istria.

Thanks for all your replies. Yes, my itinerary is spread apart. We are now thinking of doing RS tour for Croatia next year.