If the rifle is .54 caliber I would get some .530 diameter roundball. If the rifle is a .50 caliber then you will need some .490 roundball. Hornady, Speer, or Buffaloare a good brand. You will need some pre lubed patches in the matching caliber .015 thickness. Since this is probably a percussion cap rifle get some #11 caps. CCI Magnum caps are good ones. If they have RWS 1075 I like them better. Just so you know, you might want to purchase the caps and powder somewhere local and not through the mail because there is a $25.00 haz mat fee to ship the stuff to you. As for powder, since you're starting out, any of the major brands will work fine for you. Triple Se7en FFg, Pyrodex RS, American Pioneer FFFg grade, Black Mag3, Goex, Swiss, Pinnacle FFFg, any of these will work fine for you. Since you are starting out and might be shooting a lot, get some of the American Pioneer Powder or Triple Se7en. They produce less fowling in the bore and you should get excellent accuracy. You might also want to pick up a bag of wonderwads. Sometimes when shooting Triple Se7en powder, the patch will get smoked but the addition of the wad between the powder and the patched roundball will solve all of that.

You might find that the projectiles load too easy. In that case you can increase to a .535 or .495 diameter roundball but usually the other size will work well. If you want to shoot conicals, then get some T/C maxi ball 370 grain and a tube of bore butter....