Most of this has been said already. But 220 is where you want to stop for browning. As it was described to me, the rust needs something to hang on to. For hot browning, it will take 3 coats (at least) to get it fairly even. Let the first applications sit a couple days between coats and then rub...
I concur with the $400 value for the two barrel kit. But also could see where an "Enthusiast" would not blink at $500. So based on replies here, if it were me I would advertise it for $500 to start. Reduce the price as necessary to secure a sale.
Just had an outing with my pistols, Usually I shoot .490 balls but all I had with was Hornady .495. I about destroyed my hand trying to pound them into the barrel. So I decided to measure everything when I got home. The .495 consistently measured from .497 to .499. So then I measured my .490...
That I am not sure of. But keep in mind, most kits are just an assemly of parts. You could go through a company like Pecatonica and get a barrel and pre-carved stock and then just have the ramrod hole drilled. It is not terribly difficult to embed a lock.
For me it is too shiney. I like a satin finish so I tend to go with an oiled and waxed stock. But if you like more of a gloss, Tru-oilo is a nice finish easy to apply.
I found a book in the library written by one of the curators? It was originally located just north of Asheville NC. They had a rifling machine and some examples of Mountain home made guns. Not sure if that stuff made it to TN.
You have a great trip planned. If you happen to be in Asheville and have time to shoot, visit the French Broad Rifles. We shoot on the second and fourth Saturdays of each month. You can p.m. me if you need further information. Johnson City-Jonesboro is nice, my Daughter went to school up there...
My experience has been that if a range allows you to shoot black powder, that instantly drums up interest. Especially a flintlock! Use that as a foot in the door to offer a mini-session on muzzleloading. Many large ranges have a muzzleloading contingent.