I'm not sure what I'd do with it yet, beyond target shooting and plinking,... I definitely am interested only in percussion, not flintlocks.
I'd recommend that you start with a .44 caliber Remington 1858 made by Pietta, in the 5.5" barrel version. Well made and reliable shooting.
For a rifle, right now the Lyman Trade Rifle in .50 caliber is probably the very best value. That's the overall price (on sale now), with the quality and accuracy.
Traditions makes a couple rifles very close to the Lyman Trade Rifle in price, but I think Lyman edges out Traditions in quality in that caliber.
For a rifle, should it be a traditional design, or a modern inline model? What caliber is best for casual target shoting/plinking? I don't want to spend a fortune on bullets; is any particular caliber the cheapest to shoot? I haven't seen any rifles below .45, are smaller calibers easy to find? Do they cost more?
For the revolver, round ball and caps and felt wads are inexpensive. You will need all lead round ball in .451 size. Sorry to say that revolver bullets and rifle bullets normally don't interchange when talking muzzleloaders. You can, however, use the same size black powder for plinking and targets with the rifle as you do in the pistol.
As for rifles, the modern inlines often costs less, but they will have rather crude iron sights in many cases, as the manufacturers assume you're going to hang and optic on them, and this then drives up the price.
Hands Down the cheapest thing to shoot is a patched round ball and most inlines don't shoot the patched round ball well. You're talking 25 cents a shot for .50 caliber using store bought components when shooting a patched round ball and the lowest recoil as well. Inline ammunition is more costly.
You will pay a little more, but if you want the lowest recoil, cheapest shooting, plinking and target rifle, Traditions makes the
Crocket in .32. A little bit more care is needed in loading, but it's easy to master, and a lot of folks like this rifle as it's akin to a modern .22 in many ways.
LD