I had some some powder go bad in a my revolver before, took the nipple of, picked at the powder, dumped it out, put some fresh powder back in, rammed the ball down to make sure it was tight, capped it up and fired away. I was a little scared though, you could attach a string to the trigger or something and go a distance off and shoot it so you dont have to hold it. Once you take the powder out look to see if there is rust behind the ball in the chamber.
Dont get a starter kit, the flask is nice to have, the measure looks good, the capper will be useful (I dont have one) but I dont know about the nipple wrench. You want hardened steel wrenches, I'll give you a link to a good one. Also the starter kit isn't worth it, you could probally buy some balls from someone on here or over on the castboolits forum, or at cabelas or any store like that. Cabelas has a good price for pyrodex black powder subsitute, and they also sell caps. the lube or wads isn't totally necessary, it just keeps the fouling down. People claim it prevents chainfires, and some say chainfires occur from the nipple end. it's a big controversy in the black powder world.
As for the '51, they are classic C&B revolvers. They do put them on sale if you wait, they had them $180 at Christmas. Colt black powder revolvers do hang up though, the hammer pulls the spent cap of each nipple sometimes on some guns. The remington 1858 doesn't do this.
If you really have to have lube, you could buy some unsalted crisco at the grocery store.
Have fun! Once you start shooting black powder, there's no going back