A technique which worked well for me on the B707, B747 and B767 was to adjust seat/rudder pedal reach so that with my knee locked I had about 50% rudder applied, more on B767 naturally, and adjust input by rolling my ankle forward or aft. Sounds complicated but it really works for me. No half extended leg to get tired or cramped. It really works a treat on B747, allowing for inbd or obrd engine out. It works on PA 31-350 too.
As for how much rudder - just look out the window and stop the world moving sideways. Don't overthink it, do what comes naturally.