I add DEF fluid at every oil change which is typically 2 gallons using only DEF from a container and at 96k miles no issues to date. And for the naysayers it doesn't mean I would have problems using bulk DEF, but I'm just more comfortable with the container stuff.
Running exhaust brake is still a common practice on the 6.7 cummins to prevent soot build up in the turbo, but not a good idea when driving on slippery road surfaces.
B20 is accepted but draining the water separator more frequent wouldn't hurt, but is not required by the mfg.