Nice rifle! Daryl should be along soon with better ideas than I have, but FWIW:

My notes--put together back when I bought what I thought was an 8 bore that turned out to be a 6 bore--say 10 drams with ball. A dram is, IIRC, 27.3 grains, making the charge ~270 grains. The velocity mentioned was around 1,500 fps.

Assuming pure lead, a ball measuring .830" should weigh 860 grains. This would make the charge slightly more than 1/3 the weight of the ball. A couple of the early writers mentioned using charges in the neighborhood of 1/3 ball weight.

Powder choices are somewhat limited by availability, but 1F or 1 1/2 F Swiss would probably be the best places to start. Honestly, I'd start low (~150 grains or so) and work up to my recoil tolerance/accuracy/trajectory matching the sights.

For patching I'd probably go with 10 ounce canvas duck, washed a couple times to remove the sizing. If I couldn't conveniently source any (or couldn't wait) Key brand overalls (from the nearest farm supply store) are close. For patch lube, I'd try neatsfoot oil, olive oil, or mink oil.