First things first, clean the dickens out of the bore. Don't know what kind of "grease" they use in it, but it's tough and your accuracy won't really develop till it's gone. Takes several good cleanings and shooting to do it.
I started out with .530 and .535 Hornady balls, Oxyoke WW patches in .010 and .015, plus .018 ticking. Right off .530 and .010 were too lose, .530 and .015 was fine, as was .535 and .010, while .018 patches were too heavy for either. After 200-300 shots the .535 and .015 took the lead in accuracy, with .530 and .018 right behind.
Initially I couldn't even start .535 and .015, but as things got easier using the prior combo, I tried again. Took a sharp slap on the short starter to get it started, but man, what an improvement in already good accuracy.
A good starting load, and one which you are likely to use for target or small game with some adjusting is 50 grains of 3f or 2f, whether the real stuff or pyro. My deer hunting load is 90 grains of 2f, and my moose load is 110 grains of 2f.
A "good" nipple is one that fires all the time, whether original, a Lyman replacement (worked for me), or one of the alternative "hot" nipples. Remember that the Lyman takes a metric nipple, as I recall something like 6x.25mm, rather than US standard.
My original nipple required a whole lot of force to seat the cap all the way down and prevent misfires. I could tell instantly that I hadn't seated it far enough, because there was always a misfire. The replacement from Lyman didn't require as much force to seat a cap, and any misfire is a result of too many shots without picking.