Not to put the cart before the horse, but I wish I had put some thought into what I was going to do with my guns before I bought them as a couple suggested you do here. I had no idea what was available as far as competition (and fun) in muzzle loaders and black powder revolvers. I don't regret buying any gun I have bought, but I could have been better informed. Depending on what you buy, you may not be able to shoot some matches that are "as issued". Also, there are some winners as far as what really works well with the good shooters. If you think of shooting in terms of shooting a match, and find out what winners shoot, you will more than likely be happier with what you buy even if never getting further than plinking.
I think the .36 or .44 Remington new army is sound advice for a starter gun. I got one from cabelas in .44, I got the "target" model. Sights are very hard to adjust, although it's a good gun if you can get it adjusted to where you need to shoot. Had I gotten a .44 or .36 with non adjustable sights, I'd be better off for shooting "as issued". I'll probably get a Ruger Old Army at some point with target sights and an uberti Remington new army in .36 caliber. If you are target shooting, it is likely that you can get away with less powder with a smaller ball (if all other things are equal and you aren't shooting too far) and still get accuracy. I can shoot my .36 for about .12 cents a round, after buying lead, casting equipment and caps. My Remington is about .15 cents a round, the way I have it figured, as the powder charge and ball are both heavier.
I like my 1851 Navy by Uberti. It is a .36 and until today, I hadn't shot it much and didn't care for it's accuracy. Today I put 40 rounds through it, and filed the sights to get it on target a little better. I was impressed with the accuracy of the gun with 10 grains of powder (down from 15 grains) a .357 case full of corn meal and a .375 ball. Adjusting sights is slow for me, but I don't want to file off too much and have to buy a new hammer.
Dixie Gun Works is where I would buy from. My Uberti came from there a few years back, I think. I bought it second hand.
So much to buy. So little time.
Take a look at
www.nmlra.org. Find some local shooters. Have fun.
I went to Friendship Indiana this year to see the National Championship Shoot. Wow!