Caulk and paint. Use filler if gaps wider than 1/4inch.

Always done this and if done right, will last 20 years before needing to be redone.

I use Abatron and PC Woody, depending on the application. Use a drywall knife with rubbing alcohol to shape. Obviosly remove all of the soft wood and treat with wood hardener like PC petrifier first.

Depends on the extent, size and location, then Interior vs exterior.

If it's a large span I'd shy away from relying on filler - you could isolate the rot and fill with a dutchman in some circumstances.

what products do you think work best?

Bondo? Abatron?

I had tried the gorilla wood filler and it had shrunk too much after a few years and I seem to remember the same problem with DAP.