B.G.
There are so many aspects of Black Powder and CAS (I am stretching by including CAS since I don't do it myself, but I think I am right) and every aspect is fun.
I am going to make a recommendation which kind of puts me out on a limb.
I would start with a black powder revolver of your choosing (seems like you might be partial to an 1851 or 1860 pattern Colt) and move to cartridge revolvers as your appetite grows.
I am well aware that I have cast myself in disagreement with others who shoot a heck of a lot more than I do. But there is a reason.
Shooting BP is somewhat cheaper than cartridge. The revolvers can be somewhat more finnicky but I think this is a good thing. As you have already indicated, you like the looks of the open top cap and ball revolvers and so you would likely wind up with one anyway.
BTW, I don't know how much shooting you do, but don't forget eye protection and hearing protection.
Welcome to the club...Your are gonna love it.