I couldn't give any real idea about the value except to say that personally, I prefer replicas which copy some original fairly closely. If it had a steel frame and a shorter barrel it would be more interesting to me. You could browse around on auctionarms or gunbroker and perhaps get some better idea of prices.
I use Remington #10 caps on all my percussion firearms which don't take musket caps. That would be what I tried first. You can always replace the existing nipples if they are an odd size.
Pyrodex is formulated as a black powder substitute and is widely used, mainly because it's more available than real black powder. There's no reason not to use it but, again, a lot of the attraction in shooting these guns for me lies in copying the originals. That means real black powder. Real black powder will be my preference as long as I can get it even if I have to make some sort of road trip to stock up.
The most common ball sizes used in percussion .44 revolvers are .451, .454 and .457. If you can measure the chambers in your revolver, you need to choose a ball size a little larger than whatever that size is so the ball is shaved down when you load it. If you can't get an idea beforehand on the size of your chambers, I'd probably buy some swaged .454 balls to try. Those will probably work just fine but if they are really hard to load, you can get .451s next time.
You're gonna have fun with this thing!
Steve