Thanks so much for the replies and sorry for the delayed response. This is not only a hard trip to plan because I simply don't have enough time to fit in everything but because what one person says is a must, another person says is meh. In general, I've spent the last couple of days watching a lot of youtube videos of these locations and it hasn't made things easier, not because everything seems beautiful but because a lot of the places don't seem amazing (though not ugly or anything, on video they don't stand out like Florence/Prague as cities or Norway/Switzerland for nature). Zagreb, Lake plitvice, hvar, kotor... It doesn't seem like their beauty and appeal translate to youtube videos.
Texastravelmom, thanks so much for your help. I like museums, history and hiking. I avoid beaches unless they are considered "world class" and unmissable. In the past, I have taken long trips before though only in "developing" areas (3 months south america, 2 months southeast asia). I am pretty used to discomfort, long bus rides, and delays. You mentioned your love of Sarajevo which made me look into it and I aim now to include it (ha, you are probably wondering how, I have the itinerary below). It also makes Mostar easier to include.
Barbara, thanks so much for the link to the ferries! Though right now i'm leaning towards not taking any due to the time problems.
acraven, thanks so much for the info on plitvice. If I go, and I think I will since I like hiking and that seems like the best option (vs krka for example), I will try to follow your advice on the timing to avoid the crowds. I'm going in late April by the way which i don't think is the main season.
Emily, thanks for the advice. The reason i want to include Slovenia and am generally including too much is because there is a good chance I won't be back to this area for a very long time since there are so many places in the world to see that I haven't been to.
Mr E, thanks so much for the advice. As I wrote in the intro, it's so hard to figure out what to go to since what one person says is a "must", someone else says is skippable.
ok, so how about this for an itinerary with bus times that I got from Flixbus. Does anyone know if there any route I should look into taking a train?
day 1 - arrive in ljubjana and go to lake bled
day 2 - lake bled in morning and then in afternoon (around 1 or 2 pm?) take train or bus to ljubjana. So give or take it'll be like half a day lake bled and half a day ljubjana though an hour will be lost with hostel check in. Does that sound reasonable?
day 3 - ljubjana for the day and then take night bus to sarajevo (there is a 12:30 AM to 9:30 AM one and a 7:15 PM to 4:45 AM one. I am leaning more towards the 7:15 PM.
day 4 - sarajevo (so arrive at either 9:30 AM or 4:45 AM and stay the day. I wish there was a night bus that split the difference and was like 11 PM to 8 AM or something similar)
day 5 - sarajevo to mostar 6:50 AM to 9:30 AM bus
day 6 mostar to dubrovnik 7 AM to 10:50 AM bus - this bus offered by flixbus is only offered every other day so i have to make sure it aligns.
day 7 dubrovnik
day 8 dubrovnik or day trip to kotor
day 9 dubrovnik to split (possible buses to choose from are 3:30 AM to 8 AM, 8 AM to 11:45 AM, or 9 PM to 1:15 AM night before)
day 10 hvar day trip (should i do korcula day trip from dubrovnike instead? (and adjust itinerary accordingly)
day 11 split
day 12 split to lake plitvice (bus 7 AM to 10:30 AM)
day 14 lake plitvice to zadar (bus 9:45 AM to 12:30 PM)
day 15 fly out from zadar or go to zagreb first (buses are (3:30 AM to 7 AM or 7 AM to 10:30 AM) to fly from there