Were were there in August 2018 and I don't believe the entrance fee was included in our Swiss Pass. I do recall paying a fee, but thinking that it was very low for such a stunning attraction -- 10 Swiss francs I think. We bought our tickets when we arrived, so, no, it's not necessary to buy tickets in advance.

È sempre molto soggettivo e personale,direi però che in 60 minuti si fa una buona visita.

I came to Thun by train, but I did notice quite a big parking lot underneath the Aldi on Grabenstrasse (there's a Tamoil gas station in front of it). If you go to the castle via the winding road right next to the roundabout (from the Untere Hauptgasse), yes, you will walk up a steep walkway (with some steps). So if you go straight up coming from Aldi (or from the marketplace area/trainstation), the road is steeper. But the view is better :) BUT if you go around, from the other side (from the lake/mountainside, let's say), from Burgstrasse, the walk is much easier (less steep) but a bit longer. It ca be done by older people, I don't consider it to be taxing or too steep. Most of the people in the courtyard were over 60 years, but the Swiss are known to be some of the fittest people in the world :) Oh, there's a small parking lot at Burgstrasse 5, but I wouldn't count on it being free of cars in a busy day.