We are arriving in Zagreb and departing from Dubroknik 3 weeks later. We'd like to check out some of Montenegro as well, and visit Sarajevo. We've come up with a loose itinerary. Zagreb, Zadar, Trogir, Split, Vis Island, Sarajevo, Kotor, Budva, Dubrovnik. Does that seem like too much? Is there anywhere that is a must see?
I would say that I am great and fine with Saravejo alone.
Sounds like a good itinerary. However, give yourself some leeway to stop off in those incredible places you'll find on your travels. Croatia and Montenegro are not the sort of destinations where you rush around from place to place ticking the dots on your map.
I once traveled from Split to Hvar with the intention of staying one or two nights and then travel onwards to Korcula... two weeks later I was still there.
Don't be disappointed if you don't make all your scheduled stops, instead give yourself a list of destinations where you think you'd like to stop.
You'll have a wonderful time in the most beautiful country. Enjoy!