Good points so far, so I won't retread that ground. Here's some additional points:
The taper on those Lyman nipples isn't quite right for #11 caps. They sit too high and often don't actually contact the top of the nipple, especially as the nipple dirties a little. As a result you might get some misfires. This is a short-term fix and may sound a little scary, but point the muzzle in a safe direction down range and do it anyway if you are getting misfires: After seating a cap, very carefully lower the hammer onto the cap and press down on it firmly to finish seating the cap. That will cure the problem long enough to let you keep shooting, but long term you will want to replace those Lyman nipples.
Another point: That little screw between the two triggers adjusts your set trigger. In a nutshell, it's too short and you won't like the results of the set trigger till you replace it so you can adjust the trigger. Unfortunately it's a metric size and I don't remember which. Not a hassle your first time out, but you'll want to be changing that screw eventually.
Another point:
When seating a ball, be sure not too grab that rambrod too high up from the muzzle. Six inches is about right. It's sure easy to break a ramrod if you grab it too high, and a series of short strokes is better for ball seating than one long one.
Another point:
Whether shooting offhand or from a rest, concentrate on the follow-through, or what happens between the time you pull the trigger and the ball actually leaves the muzzle. It's longer than on other rifles you may have shot, and as a result it's possible for your shot to wander a bit, even if you had things perfectly lined up at the split second the trigger broke. It takes practice, but you'll learn to deal with it.
I could go on, but I'll only add one more point:
Start your shooting at around 25 yards and stay there for a while. Your wiggles and wanders will have less impact than at longer ranges, and it can get discouraging. You'll gain a lot more confidence in that fine rifle if the shooting is going well.
Oh heck, one more:
I'd probably start at a charge of around 30 or 35 grains of 3f black powder or Pyrodex P, just to get acquainted with the rifle. That's my favorite charge for mushing bunny heads with my own GPR 54 cuzz it's accurate as sin. You'll eliminate a lot of recoil and shoot it better while you are getting acquainted, and there's no sense in fighting a flinch right off the bat with your new gun. You can always puff up the powder charge to big game hunting levels later, but for now just have some fun with the light loads.