If possible, I would urge you to visit all 3 castles in Bellinzona. If time doesn’t permit, I’d opt for one of the ones other than the one in the city itself, either the highest one for the views or the middle one for the insights it offers into castle construction.

As for the funicular to San Salvatore, I thought the walk from San Salvatore to Mercote among the most beautiful of the walks I took while in Switzerland, but IIRC, it took 4 hours or so.

For your many other options in the area, you might consult the Michelin Green Guide, Rough Guide, or even my trip report:
https://www.fodors.com/community/eur...thanks-983126/

Seems to me rather odd that Pal initially said he preferred Lugano, and now says he preferred Locarno.

Well It seems to go from Zurich to Bellinzona and return is 126 CHF (full price) per person. The half card itself cost 120 CHF per person so not sure if should buy.
In Ticino if you stay in one of the hotels you get a a ticket for free transportation inside the area (i.e. to/from ascona, lugano etc). However, the cable cars will cost me as well.

OK - but figure the cost of cable cars - they can be very expensive and boats but probably not enough.