Grats on your new rifle and welcome to the forum.
Even more so, welcome to your new addiction. :haha:
That's how I started not so awful long ago... now I'm ruint for anything other than muzzleloading. :surrender:
In my opinion real blackpowder is more reliable and easier to clean up than any of the substitute powders that I have tried. There are those that will argue both points... There is, however, no arguing the fact that real blackpowder is REAL blackpowder. :wink:
I'm guessing your new rifle is a .50 caliber. Either 3F or 2F powder will work. Your particular rifle may like one over the other. You just have to experiment and see which kind and how much. Also what size thickness of patches and what kind of lube.
As far as what kind of caps, just about any #11 caps should do just fine. Get what you can find. I like the Remington brand caps myself.
Just to get started, pick up some 3F powder, some pre-lubed .015 patches, some #11 caps, and some .490 roundballs (assuming your rifle is a .50).
You will also need a powder measure, short starter, a nipple wrench, and a cleaning jag. And read a lot on the forum. :thumbsup: