As others have said, #4 buckshot works great for close range coyotes.
Buckshot is NOT for use on waterfowl.
Lead projectiles of any size are illegal for waterfowl. That's federal law. (some game wardens carry a magnet to check your shot)
Lead can usually be used for upland game, but even then, check your state regulations. Some wildlife management areas allow lead for squirrels, rabbits, pheasant, etc., but others do not.
Some states allow buckshot for coyotes or deer. Probably most do not. I grew up in a state where buckshot is legal for deer. I now live in Tennessee where buckshot is illegal, not only for deer, and coyotes, but for anything. Not sure, since I don't use it, but I think "T" shot is the largest shot that can be used here in Tennessee for coyotes.
So, as for how many buckshot pellets you load, only experimentation will find the correct result. Is your smoothbore muzzleloader choked? Wad under and over the shot? Some other combination? Powder? 3F? 2F? 60 grains? 70 grains? More? You must try a lot of different combinations until you find what works best for you in your particular firearm.
Just be sure to check your state regulations for what is legal and what is not. This could all be just a moot point if buckshot is illegal in Colorado.