Decisions, decisions; first decide what you are planning, mostly hunting and what, target shooting and hunting, percussion or flint. I recommend a percussion gun starting out. I think your choice for a Traditions Hawken is a good one but only in percussion, the lower priced locks in flint are just OK, nothing special. Traditions barrels are good, as well as accurate. Then there is the choice of shooting bullets or patched round balls, the rifling rate of twist will be different for rifles made for one or the other.
TCs made their rifles with a one rifling twist in 48" which is middle of the road, these barrels would shoot a ball or conical bullets. I owned a bunch of them and found they didn't shoot either equally well, they tended to prefer one or the other with a patched ball usually being the best. . Patched Ball specific barrels in the deer hunting calibers of .50 and .54 tend to be 1 in 66", barrels made to shoot only bullets are usually around 1 in 28". Nothing is written in stone, some round ball barrels will shoot a conical, most won't, some fast twist barrels will shoot a round ball but most won't
How deep are your pockets, the cost of M/L parts has doubled in the last few years, M/L prices have followed suit. I can have a thousand parts before I even start building a new rifle.
Used rifles are sometimes a good deal but unless you have a bore scope or a very good bore light to look in the barrel, I wouldn't buy any of them. Back in the day we all bought TCs or CVAs when states started having M/L seasons, many people treated their M/L like a modern rifle and didn't clean them after they shot them. Consequently, there are more of them out there with rust and pitting in the bore than ones with pristine barrels.
Another thing to remember is every rifle has a personality, it will shoot poor groups with one load and drive tacks with another, you have to experiment around and see what it likes.
Here is an example; I built a flintlock rifle with a .50 cal barrel and wanted a .54 so I sent the barrel off for a re-bore to .54. The guy who rebored the barrel did a lousy job, the best I could get out of it was a 5" group at 50 yards with a variety of loads.
I coned the barrel to make it easier to load, this amounts to using a special tool to make a funnel like opening at the muzzle so you can push a patched ball in the bore with your thumb. I shot the rifle after coning it and the accuracy hadn't changed.
I was shooting a little low with 80 gr of powder, I had run out of sight adjustment so I upped the powder load to 85gr, I hadn't shot this much powder in the rifle to this point.
Bingo! I was shooting low so I held high for the first shot and hit high so I went back to my 6 o'clock hold for the next two shots. This is at 50 yards, I would challenge most modern rifles to shoot this well with iron sights at 50 yards.
