Joe,
Plenty of good advice given here already but I'd like to toss in a little more. Some people dislike true black powder because it is corrosive and requires that the gun be cleaned after a shooting session. There is a mistaken impression that Pyrodex, Triple 7, and a couple other "substitutes" are non-corrosive and therefore don't require regular cleaning. The fact is that both Pyrodex and Triple 7 are corrosive. Pour some on a clean piece of carbon steel, ignite it, let the fouling sit outside overnight, and see for yourself the next day. My point is to clean your new rifle after each shooting session regardless of what propellant you choose. I use water from the hot side of the tap with a drop or two of dish detergent in it. A flush nipple set-up like Track of the Wolf sells makes the whole process easy. I can completely clean my flintlock in 15 minutes or less. It takes me a lot longer to scrub out a modern rifle.
Triple 7 in particular produces higher temperatures and pressures than real black powder. Keep that in mind when developing loads and reduce charge levels accordingly. Start low and work up slowly.
All the critters you mentioned hunting are thin-skinned and relatively light-boned. You don't need to attempt to "magnumize" your rifle to hunt them. Once the ball has gone in one side and out the other any remaining velocity and energy are wasted anyway. Like William suggested, start with grain weight of powder that equals the caliber of your rifle and work up. My .50 caliber flintlock loves 70 grains of FFFg. There may be those who will tell you that is a light charge in a .50 but for the animals available to hunt in south central Texas and the average range at which shots are taken, 50 yards or less, it is more than enough. I value accuracy above all else, the ability to put that ball right where I want it for a quick and humane kill. To me there's no difference between an accuracy load and a hunting load.
Have fun with your new rifle. Before long you will be wondering why you ever shot anything else.
Storm