RE: 00 or 000 buckshot?
I've never used buckshoot for deer but know a couple of people who have tried it. I don't what they used but I do remember neither of them were crazy about the results.
If I had to use buckshoot, I would use 000 because the pellets and heavier and larger. Personally, I would use a bow before I resorted to buckshot but that just my personal opinion.