Welcome Chaco24 to the forums.
Pyrodex is harder to ignite than real black powder (GOEX, Olde Eynsford, Scheutzen, Swiss, et al). You didn't say if you have caps, but I would want to have the hottest caps that I can find, that would probably be the Remington caps. Sometimes the pistol nipples are sized for #10 caps and other times they are sized for #11. I would use #11 magnum caps (CCI) to help set the Pyrodex charge off. If the caps are a bit large, you can slightly pinch the cap and they will stay on the nipple. You may have to watch for loose caps jamming the works, but the loose caps can easily be cleared from the action. Pistol grade powder (3fg) would be better than rifle grade RS (2FG), but the 2fg will work.
The powder charges in this muzzle loading sport are measured in volume which is equal to real black powder. Pyrodex is less dense so the measured weight is less than the equivalent weight in black powder, but Pyrodex is designed so that the volume measure is roughly equal to that volume of black powder. Yes, 2f is safe to use in your new pistol. Be very aware that the fouling generated by shooting muzzleloading firearms is very corrosive, so be sure to carefully clean and lubricate your new pistol.
Read the threads on cleaning and lubricating. A new pistol will need to be cleaned using alcohol or carburetor cleaner to get the grease out of all the nooks and crannies that will block your cap flash from getting to the powder charge. Then you want some grease on the pin that supports the cylinder. A little bit of anti seize lubrication on the nipple threads is a good step. Do not over tighten the nipples in the cylinder. Its not necessary to tighten past snug on any of your threaded bolts or nipples.
The first time you go to the range be sure to cap your unloaded gun and fire a cap on all the cylinders. Point the muzzle at something that will move to watch and see if the bore is clear. Blades of grass move, leaves flutter, or dust will blow around.
What size ball came in the starter kit. A good 44 caliber ball will be 0.454" in diameter. It is confusing, but you want a soft lead ball so that when you load the ball a ring of lead is shaved off the diameter. 44 refers to the diameter from land to land and you need the 45 caliber ball to fill the grooves. There is a long thread on this topic here on the forum.
There is no need at this time to worry about refinements on the cylinder mouth diameter or other performance improvements. This is the time determine how it shoots and where to find black powder. Yes, Pyrodex or 777 will work. And if that is all that is available there is no reason to get over stressed.
Make some smoke and put some holes in a target.