I'm not a fan of either shooting at running deer or of buckshot. First, it's hard to make any shot on a running deer, let alone a humane one. Second, it's awfully hard to be aware of what's beyond your target when you are sweeping your muzzle to follow the deer.
Regarding range, yes '00 should be limited to 40 yards or less, but you'll have to pattern your shotgun. Personally, I use slugs when deer hunting with a shotgun.