Did you go with anything yet?
The 1860 is probably everyone's favorite cap and ball. Good balancing (probably not quite as good as 51 though) and the aesthetics are terrific
That being said though...
I think the 58 is the best gun for a cap and ball beginner. Yeah, it's large and clunky but the scene from Pale Rider certainly makes up for it
1. You don't have to deal with the barrel wedge and prying the gun off everytime you clean it or prep it for shooting. If you wanted an extra cylinder or even a conversion 45lc cylinder, it's so much easier to take apart.
2. The Remington 58 should shoot low and the Colt copies should shoot high. Filing off part of the front sight is easier than filing into the rear hammer notch for most people. And if it's still manufactured the same, the Uberti 58 has a dovetailed front so you can tap for windage.
3. The cylinder is larger and will accept more powder than the standard colts (buy steel frames as everyone has said). But that may not matter to you.
The general word of wisdom is to buy the gun in person or from a store that will stand behind the product; preferably in person because you may have to go through 2-3 guns before you find one that isn't broken straight from the factory
You get a good one though, it's good for a long long time.
I'd personally use Triple 7 over black powder for maintenance purposes. Blackpowder gums everything up and you'll have take the gun apart frequently at the range. With triple 7 you might have to quickly wipe it with T/C bore cleaner milk once during your shooting session, if at all.
Plus, I have gone 2 full weeks before cleaning my guns after 777 and they cleaned up good as new (not a great idea to do with black or pyrodex...3 days is stretching it). Your mileage may vary as I wouldn't put out a blanket recommendation on that (especially if a gun has some minor pitting already).
They are fun and you probably will want one of everything