With .011" rifling, I'd be thinking round balls only. I'm sure they'll shoot well with whatever powder charge you decide upon. I'd start at 3 drams and go up from there, 1/4 dram to 3/8's at a time until you get the accuracy and regulation you want. 4 drams (110gr.approx) is not a heavy load for a 14 or 16 bore rifle, but with a hardened ball, should make a smasher for any game in NA. I personally like 1,500fps to 1,550fps for the flatter trajectory - giving a point blank range of 120yards. It may take 4 3/4 to 5 drams to get that. Recoil may be the deciding factor. Too, you most certainly do not want to break the stock.

I have used once (or more) fired plastic 12 bore cases for 2 or three shots with full 7 dram loads, so feel any plastic 14 bore cases should be useable as well.

I wouldn't worry about the twist - the fairly deep rifling will hold a patch ball well. My 14 bore muzzleloader gets superb accuracy to well over 200gr. of 2f in it's 66" twist. My accuracy loads run only to 165gr., though. Easy enough on the shoulder and still fairly efficient per grain of powder. It takes a lot more powder to get much of an increase in velocity.
The Lyman .662" mould casts right at a 1 oz. ball. Use of a 12 ounce Denim should be about .025" per side, giving a bit of compression in the bottom of the grooves. You might not be able to use that heavy a patch, BUT - use as heavy as you can & perhaps a card wad between powder and patched ball. I'm sure you'll be happy with the results.

Here's the recoil at the top of the muzzle's travel. 5 dram charge with a 14 1/2 bore (.682" @ 482gr.)ball - 9 1/2 pound rifle. Before and after the shot. I was aiming at a 200 yard target for a 'postal' match.