Istria area

We loved Rovinj. Spent 4 nights there. We found a great room with private terrace looking over the harbor on VRBO. It’s been since 2017, so you need to track it down.

One thing. Do not miss the stained glass in the local cathedral. It’s very odd that we find very little information about them, but we found these to be some of the best we’ve seen anywhere! Very modern art looking not traditional at all.

Have you deducted how much time you will spend in Split?
It's about a five hour drive to Rovinj, but you need to determine how many places you'd like to stop. It may not be worth driving all the way to Istria.

I'll be looking for an overnight stop between rovinj and split if you have suggestions.
Plan is now to fly into Zagreb then drive straight to rovinj. I think it's like 4hrs

Where are you flying from? Four hours is a bit much if flying overnight in economy. Opatija is still two hours, but I would recommend that over double the drive. Or leave the next day.
Once you are in Istria, distances are not great, so you can group some of the little hill towns together for day trips and choose based on accommodations you like.

Opitija actually sound like a nice little stop along the way. We have long flight from usa but we get in around 1 pm so by time we get luggage and car, probably closer to 2:30 by time we get on the road. (does google maps work or do I need to rent the gps). Know any hotel recommendation. Doesnt need to be expensive since just one night, but was planning on maybe going to Rabac for a day trip anyway. Always nice to find a local tavern with some local musicians.

Are there any places we should avoid, unsafe for travelers?

Google Maps works fine for me--when having a passenger do the navigating anyway.
I stayed in the Hotel Ambasador, nto charming just modern, was fine for a night but look on Booking.com and select parking.
Next door Lovran is nice also.
Croatia is a very safe place, I would have no concerns.