The size of the ball for a Bess depends on whether or not you are loading for speed as in a combat situation, or for accuracy as for hunting. For speed, since they did not stop to clean the bores, you use a very undersized ball in a paper cartridge. Many of the folks that I know who shoot "speed matches" with muskets use a .675 ball, and some even as small as .662.
For hunting and marksmanship, folks use a ball much closer to the bore diameter, so as folks have already suggested, measure the bore to be sure. Some folks use a .715 or a .690 ball patched.
Some folks have found though, that a bare ball, on top of a wad with some newsprint over the ball is actually more accurate than a patched ball in a smoothbore. It's odd, and shouldn't be that way, but some folks find that a .735 ball bare works better over a wad than patched.
Finally, some of the speed shooters use the same small ball for hunting, but they make a paper cartridge with an especially thick wall to snug up the ball when it's in the bore, so instead of 2 wraps of the paper with a .675 ball, they might use 5 wraps. Now you'd think that a paper cylinder to snug the ball up closer to the bore diameter would work like a cloth patch, but it seems to work better. Perhaps it's the fact the cloth has to form folds around the ball, and since there are no grooves the folds are not consistent. I don't know, but I know of several folks who shoot in "marksman" competitions, and none use a cloth patch around the musket ball.
Now as for powder, 80 grains is 3 drams and is plenty for hunting. Folks doing speed drills as per British drill, use 90 grains, for they pour about 10 grains into the pan, then load the musket..., not recommended as it's not safe. Better to go with 80 grains and then prime the pan after loading the main charge.
There isn't much difference between pan ignition between 2Fg and 3Fg, but 3Fg works better in blank loads, so many of the guys who use the bess for reenactment and for hunting use the same size powder for both. It's not a normally recommended granulation for such a large bore, so the recommendation for folks who shoot targets or hunt is for 2Fg for live-fire loads. Most folks prime with the same size powder, and do well.
I would not use 4Fg in a Bess. The pan is not of a "weatherproof" design, and that really fine powder may leak out as one walks in the woods, and I have always found juggling two sizes of powder over complicated, especially in a huge lock like that of a musket. 4Fg is great in a "small" rifle lock, but not a real advantage in a musket (imho)
LD