Usually, the Maxi Hunters will work quite well in a .54 T/C Hawken and they are reported to be very effective on larger game. Personally, I think a .54 cal. patched round ball will cleanly kill anything you will likely be hunting. The Maxi Hunters may be over kill, but they are good bullets if that is what you want to use. Whether or not a substitute powder will work in your rifle will depend on whether or not it is a caplock. If it is a caplock, it will shoot the substitutes very well. If it is a flintlock, it won't shoot subs at all. A flintlock must have real black powder. As for the substitute that the seller gave you, I think I might use it just for plinking because subs have a finite shelf life and you probably do not know how old that stuff is that he gave you. When you get down to serious shooting, you will need to get a can of new powder. Shoot the subs if you must but real black powder is always preferable if you can get it. As for the lube, there are a ga-jillion recipes and just as many people who will tell you that theirs is the absolute best. If it were me, I'd just pick up a tube of Bore Butter. It's good stuff. As for the best powder charge, no one can tell you exactly what your rifle will prefer. You will have to determine that for yourself by trying different loads at the range. Start with something around 55 grains of 3f. It is best to shoot one round into the bank first just to foul your barrel. Then run a damp patch in and out in one stroke with no pumping. Do this between every shot to keep your bore exactly the same from shot to shot. Shoot five shots from a sand bag rest at a target at about 50 yards. As long as your shots are on the paper, do not change your point of aim. Aim dead center on the bulls eye for all shots. Don't pay attention to where they are on the paper just yet. Once you find the best load, you can adjust your sights to put the point of impact right where you want it. Then increase your load by 5 grains and shoot five more shots. Keep doing this until you get to around 110 grains. Then measure each group to determine which charge gives you the best group. That's what you ought to use in your rifle. Now, if this charge is not hitting exactly where you want it, now is the time to adjust your sights to put your POI just where you want it. :hatsoff:
BTW, MSW gave you some excellent advice. His recommendation is the best source of accuracy information that you can get.