we did an UBER from town. I would rate it as easy for a fit adult and challenging for a child or an elderly person. I would keep a close eye on any children if I were hiking in this area. Many drop offs without barriers.

Yes

No taxi rank. The people I saw had transportation already waiting for them.

In fact I do not know the regularity because, in fact, it depends on the season. On summer time you have more buses..

The bus will drop you off near the fort. It’s about 100m to the site entrance.

Yes. Roman ruins old Salona.

You can easily spend a couple of hours here and if you research them you can find the areas used in filming of the series but also could get round it quickly if you wished. We went round twice just to make sure we took everything in. Enjoy your visit.

There is a big enough parking place nearby, we left our cars there, there was no problem or incident. I honestly believe it is safe for you or anyone to leave the car there. We had our own car, Romanian number and Hungarian number, nothing happened. The whole visit took and hour and a half as we were a group of 12 and took a looot of pictures. If you don't leave it there over night, you shouldn't worry.

I was there with my rental car and have not seen any bus. But I found someting on Google - just search for " bus split klis" This is a bus from split to Klis. Please be aware that the fortress is above the village of Klis

I think it would be fine as there aren't very many steps! The entrance is more of a hill and you could walk around the fortress at your own pace :)