Just returned from a trip Paris, Zurich, Venice, thorough Slovenia to Croatia, Montenegro and Bosnia.
We rented a car in Zagreb and drove down the coast to Montenegro. You might want to take a look at my report posts on Zagreb, Montenegro and Bosnia.
How are you getting to Dubrovnik? EasyJet has a flight from Paris/Dubrovnik for $35. (2 hr flight.)
The roads in Slovenia, Croatia, Bosnia and Montenegro are just as good as the roads in the states.
If you fly into Dubrovnik you might want to take a cab/bus to Montenegro. It's about 45 minutes. I would suggest renting a car in Montenegro and making Montenegro your base.
Things you should know about car rental. If you rent the car in Croatia/Dubrovnik and drive to Montenegro you will have to pay "crossing the boarder in a rental car" tax. If you rent in Montenegro you don't have to. (We rented the car is Zagreb and had to pay over $100 for the tax.
Insurance - Do not buy insurance in advance. Your American or credit card insurance is not valid. We a $150 for the insurance when we booked the car in the states and they would not give us the car. (This is NOT a scam.) We had to buy insurance again when we picked-up the car. (We got our money back with an apology,) They have two options for insurance go for the higher price everything is covered option. About $200 and much better coverage. If anything happens to the car you are fully covered.
English is spoken everywhere.
Crime/scams/beggars - Almost none. Saw one beggar. Young kids were out until midnight.
So now you are Montenegro. We stayed in Herceg Novi you should be able to find a nice 1 bdrm private apartment for $50/ night. We paid $35 and were a block from the water.
If you want to see Dubrovnik, it's about a 45 min drive.
Bosnia, Trebinje - 45 min/1 hr drive. Well worth visiting. Go to the old town and the walled city and the church on the hill.
Kotor and Tivat about an hour. Tivat is where the billionaires are docking their James Bond mega yachts, Worth walking around and prices are very affordable.
Budva and Sveti Stefan about 2 hours.
Boat ride to swim in the Blue Cave and submarine base 45 min/hr. Well worth visiting and/or swimming in the cave.
Albania - 3 hrs.
Tara, Europe's Grand Canyon 2.5 hrs. Destination for our next trip.
Dubrovnik, Kotor and Budva are all walled cities and there are many more. Dubrovnik is very good, but it can be crowded like Disneyland. And when the cruise ships arrive.... Kotor is good, smaller and you can hike to the top of the mountain. Once you see couple of walled cities they are all alike.
You might want to consider Split, Zadar and Zagreb.
Hiking - Don't miss Plitvice. Rick has a video and I just posted an in-depth report. Wonderful place to hike. (Enter at No2.) We spent stayed for 6 hours.
Pula - Wasn't on our agenda, but came highly recommend.
The mountains in Montenegro, Bosnia and Croatia are just stunningly beautiful.
Hope this helps. PM me if you have any questions.
Have a wonderful trip and happy travels.