I think you're moving pretty fast and packing up/unpacking a lot for a honeymoon. Specific issues I see:
Seeing Plitvice Lakes National Park on your way from Split to Zagreb is the worst thing you can do. It's essential to stay in or very near the park the night before your visit so you can enter the park at its opening time. It gets absolutely blasted by mid-morning, and it will seriously affect your enjoyment. (I know this because I was lucky enough to see the park twice in the 1980s and foolish enough to day-trip in from Zagreb in 2015. Not remotely the same experience.) So that's the #1 thing you need to fix. If you can get to the park mid- to late-afternoon, you can see part of it late that first day and just finish up the next morning. The sell 2-day tickets, and I've seen a comment or two about the in-park hotel(s) being able to do something to make a one-day ticket valid the next day. I don't know anything about that.
I enjoyed Istria a lot. You'll only have about 1-1/2 days there, which won't give you much time. I think of it as more a minimum-4-night sort of area.
You're allowing no time for Venice at all. You're day-tripping to Lake Bled on August 8, then hot-footing it to Venice late in the day to fly out the next morning. Many folks have found it difficult to fly home from Venice without needing a crack-of-dawn flight that necessitates expensive private water-taxi transportation to the airport. You may be luckier if you live in a fortuitous US city, but do check the flight options before getting wedded to this idea.
Rather than renting the car in Italy and ferrying it to Croatia, you could fly to Croatia and go home from Zagreb. You wouldn't have to cut Ljubljana/Bled out of your itinerary; the two capital cities are quite close together.
If you rent in Croatia, be sure to clear the foray into Bosnia-Hercegovina with your rental-car company. If you rent in Italy, clear the whole itinerary. I have read on this forum that taking rental cars on ferries is often not permitted.