Your first question to answer, is do you want a scope? If yes, then you need an inline.
If no, get a Lyman Great Plains Rifle, or a Thompson Center Hawken, in .50 caliber, and shoot patched round balls. You already want to use black powder, so this will give you the same hunting rig that the pioneers had before the Civil War. This is the cheapest shooting you can do.
You are too concerned with barrel length. Once a muzzle loader barrel gets past about 22 inches, you are getting about all the power out of it that can be gotten. I recall that the TC is 28 inches, and the Lyman is 32. Not much difference, just depends what feels comfortable to you.
As for penetration on round balls; don't worry. I have killed 14 wild hogs and deer with round balls and got complete pass through shots every time. Kind of bugged me, because I wanted a recovered ball to inspect. I was using the TC Hawken on most of those shots, with 80 to 90 grains of black powder. Remember, the elk herds were exterminated from Kentucky in the early 19th century by patched round balls.