Treblig,
I'll be hunting private land again. A lot of cornfields (which I don't care for) and some weed and switchgrass fields (my favorite). I'm bringing my Lab. She's recieved most of her training with pheasant and quail being the focus. I believe we had this same conversation last year.
+1 on the backup shotgun. I'd never drive that far without an extra gun. Heck, I don't go local without a backup.
For shot size, I've been happy with #5s the last several yrs for early SoDak pheasant. Sometimes I shoot 6's as well. I haven't shot any 4s since about 20 yrs ago in the early season in SoDak. I hunt mainly with a 20 ga with a 1 oz load.
I've never really figured out if the ditches count as "state" land and require non-tox.