A good shooting target flintlock gun consists of a quality lock, better quality barrel and if the person knows how to plan the trigger any cheap trigger can do. If you want double set triggers, even those are not particularly expensive. You can make a winning target gun with a good lock, good barrel and a knotty 2x6 from the lumber yard. I have seen too many rifles made of $700 dollars worth of quality parts and once put together couldn't get $400 for the whole works. I have seen a few positively museum quality works of art from beginners, but the odds are "agin ya."
Long rifles are a learning obsession. Learning the schools, the quirks of each school and style, and being able to duplicate a classic gunsmith of 230 years ago is something to accomplish. There is so much that is not apparent at first to beginners. The lock size, the face of the lock, the placement, the number and style of lock bolts, the inlays, shape of the butt and what buttplate is consistent with a certain builder, how thick or slender is the wrist and forestock. How to proportion and achieve that graceful line is something else again. There are people who study the differences in patch boxes and their construction. Some can tell the style and type of engraving by how the graver was tilted at certain points in the curves.
Build a gun, learn the basic skills, study as you go, then give the gun to a grandkid and start another for yourself.
There are folks out there, who are so into it, that they BUILD a gun. Hand forge the lock, the buttplate and trigger guard, even those who make their own barrels.
Building a muzzleloader is like the layers of an onion. Your can use a few outer layers or really get in deep.