Loading a longer barrel is no problem, you slightly tilt the gun, pour your powder in, seat the ball and patch just inside the muzzle then tilt the rifle more to ram them home. The barrels on Tennessee full stock guns a typically pretty long, I own a .36 SMR with a swamped 44" barrel, and a Kibler SMR that has a 46" barrel and I have no problem loading at 5'8" tall.
Barrel length, straight, tapered or swamped are aesthetic decisions you make while planned your project. A straight barrel is quite nose heavy, a tapered slightly less in the overall weight and nose heavy aspect, a swamped barrel is balanced much better than either, and is the lightest of either of the others - all of them will shoot well. If you are going with a 36" straight percussion gun then give some thought to a half-stock style, if a full stock is what you really want - go for it.
dave