Cossack: You've been given a LOT of good advice here. These guys above really know their stuff. It is summer here in Montana in some places, still some snow in my yard trying to melt but it is shooting season and rendezvous. You sound antsy to spend your money but heck, go to some shoots, many folks will generously let you shoot their rifle and look, listen, watch, ask and don't get in a hurry. You've lived this long, so snoop around first.
And if you read the hunting regulations closely, Montana does not have caliber restrictions for rifles, (for the general big game seasons), only in weapon restriction areas ( shotgun, archery, muzzleloader) (.45) If you lean toward .54, you might be better off if you bump into an elk or draw a moose tag. imho, shooting muzzleloaders is a life-long apprenticeship. Some (many folks) think you have to start with a cap gun and then move up to a flinter. Get a GOOD flintLOCK, learn to make it dependable and you'll never look back. Just my 2 cents worth. Welcome to the ALR and good luck hunting with a flintlock long rifle.