Croatia Itinerary Help - Beach Route vs Inland

I would go with Option 2 only because of your very limited time. It would be much easier to just stay in one location rather than bounce around. However, if you are comfortable with bouncing around, I would fly into Split, see Split, Plitvice, and Pula. There isn't time for much else.

I like to stay put and take day-trips rather than changing hotels a lot, but I'm not sure Plitvice is practical as a day-trip from Pula. If Plitvice is a must for you, check your transportation options very carefully before committing to Pula for the entire stay. I think you'd probably have to take a bus tour. I'm not sure about the cost, or about how much time you'd have to walk around the park. I'd consider 3 hours free at the park (not time spent in a potentially long line to buy tickets) to be a minimum. 4 hours would be better, and more time would be a plus.

I'm not sure when you're traveling, but Plitvice was mobbed when I arrived at 10 AM on a Friday in late August 2015. It affected my enjoyment of the site, though certainly it was still beautiful. It would be far more pleasant to spend the night in the area and see the park early, before the day-trippers arrive. If that's not an option for you, I'd be tempted to try a Tuesday, Wednesday, or Thursday tour. But you want good weather.

I am planning on renting a car so I am not too worried about the commute.

OK. That helps. But Rome2Rio estimates the Pula-Plitvice driving time at 3:40. Not sure that's a bankable estimate; there's a good bit of country-road involved--maybe a lot; I traveled from Zagreb rather than Pula. With a car, I'd drive from Split to Plitvice and spend the night there, planning to hit the park early the next morning. However, I'd be ready to alter my plans if the weather forecast was not good.

If there's extra time on the travel day, you could stop for a few hours to see Zadar. Rome2Rio says that stopover would add less than an hour to the travel time, but I'm not quite that optimistic.

I enjoyed Zagreb a lot, but it's out of the way for your origin and destination, and there's plenty to see on the way to Pula and in Istria once you get settled there.

are there any islands//beaches near Pula that would be worth visiting?

I am not a beach person, so I can't help you there. Rovinj is a very, very popular coastal town in Istria (north of Pula), and I have a strong suspicion that nearby beaches are a factor. I don't know for sure, though. Rovinj's historic district is really nice, and I recommend the town highly. Expect to see a lot of tourists, however. Porec has a completely different style of architecture (more colorful) and is also very much worth your time. Also full of tourists.

There are islands off the coast not far from Pula, but it appears that none of have ferry service from Pula itself. A lot of the ferries depart from Rijeka, but if Rome2Rio can be trusted, there's a car ferry running about every 2 hours from Brestova (a bit over halfway to Rijeka from Pula) to Porozina on the island of Cres. Of the northern Croatian islands I've only been to Rab. It was a quick trip made decades ago and I didn't have a car at my disposal, but the island seemed nice.

As I just mentioned in another of your posts, for the best beaches near Pula, explore the Kamenjak peninsula. Lots of secluded, beautiful spots. Find the Safari Bar - it is awesome.