Ive taken deer with mine at 100 yards with just 45 grains of 3F. Its the same load I use in N-SSA competition. Yer group size will let you know the amount of powder the musket needs then adjust sights to the load.
Best way to get yer minie balls is to cast them yerself. Buy a mold from Lee, Lyman, RCBS, and others. They arent hard to find. Order a sizer too, so you can properly size them. They MUST be properly sized to the barrel. Each barrel is differant. Fortunately I use Whitacre barrels in all my rifles and carbines so mine are .577 in diameter, 1-72 rate of twist, with progressive depth riffling.
oh and you dont use wads or patches with minie balls, just dip them in lube and shoot. They expand inside the barrel when fired. which is the reason why you need to size them properly. If the minie is to big it wont fit, if its to small you wont get accuracy and you risk blowing out the skirt. 1-2 thousandths under (max of 3) and you wont blow out the skirt and you'll get accuracy.
you really dont need alot of powder. target and hunting loads are 40-50 grains, service load is 60-65 grains. most I ever used was 90 and it was just a waste of powder, my group was 6 inches high at 100 yards. So no need for me to use any more than 45.
Lube can be simple as simple as Crisco, But I prefer Beeswax and olive oil.