I would hope you do a well researched business plan before investing a single $1.
In the fifteen years I've been an FFL I've seen almost thirty brick and mortar gun stores in a 25 mile radius go belly up. It can't be for lack of people....there are three million people in that 25 mile radius.
Black powder/muzzleloading supplies are an inventory black hole. Same with reloading supplies. Not every guy that comes into your shop is there to buy, he's there to ogle, fondle your inventory and ask questions......then he goes home and orders it online for 20% less. If you have a wide variety, you are going to be sitting it it for a decade. It will gather dust.