From the OP:
I think I need:
1. Some sort of black powder. No idea what brand or type to get. Or is it all the same? And how much - i.e. X shots per pound?
I've shot Pyrodex RS (2F equivalent) for 35+ years and have had good results. Black Powder seems to be somewhat hard to come by these days. Triple 7 is another option and there are a couple more. For me, Pyrodex does the job and is easy to come by at the nearest Sportsman's Warehouse or Bass Pro.
Shots per pound are dependent on what load charge you're putting under the projectile.
2. 50 cal projectile. Does MBC or ACME or someone make a coated one like the Hi-Tek? If so is that better so he isn't handling balls of exposed lead?
As noted by other's....this really is a non-issue. Have him wash his hands afterwards and he'll be fine. I'd be more concerned if he casts his own ammo in high volume and at that point would have his PCM run a blood panel at his annual exam to see what lead levels are.
3. Also for 50 cal projectile, round ball only option for that? What would be appropriate for hunting our smallish NC deer? Do they come in different grain weights or is a ball a ball?
Since the twist is 1/66 it's ideally suited for round balls. Most .50 cal round balls are 176 grains+/- and can drop a deer no problem within 75 yards on a well placed shot. Since it's a Kentucky Barrel its prob around 32/33 inches and that would mean the ball is moving at around 1469 FPS at the muzzle and 1082 FPS at a hundred yards with 90 grains of black powder. That's plenty to drop a smallish deer. I've crumpled 175 pound North Dakota corn feed does at approx 50-75 yards repeatedly with a round ball.
You CAN shoot conicals/sabots but will have to experiment with different weight's due to that slow twist. You might find something that surprises both of you with how accurate it is. I'd start at the lower end of the projectile weight spectrum with that.
Round balls require patches. They're cheap so buy a couple of thicknesses. As noted before, with a .490 ball go with .015 and I'd also pick up some .010's and again, experiment.
4. Percussion cap. Again, brand/type/doesn't-matter-all-the-same?
Most STANDARD sized nipples accept #11 caps. But, I don't know if someone replaced you're so I can't guarantee that. I replaced several of my traditional muzzleloader #11 nipples with musket versions. That's to ensure a hotter flash and more reliable ignition. Truth be told I keep my flash holes clean and never had ignition issues with #11's. BUT....those musket caps go off with authority.
5. Is there supposed to be some sort of patch that goes in with the ball/projectile? If so, what am I looking for there?
As I mentioned earlier above...for round balls yes, patches are required. Patches come dry or prelubed. I use Crisco or TC Bore Butter. Put the Crisco in an old 35 mm film container....black with grey top...remember those? Pretty handy for that purpose.
Here are the bare basic accouterments (tools) required to shoot that muzzleloader.
Short or Ball starter. Once you place the ball on the crown of the muzzle with a patch you need to get it started down the barrel. The short started (on the right) does this. It doesn't flex and won't break like a wooden ramrod could. Plus the ball on the end is very comfortable to grasp. You will appreciate this tool once you've fired a few balls and the barrel begins to foul as as starting the ball becomes harder and harder unless you constantly clean the barrel. The ball on the left is to screw into the end of the ram rod during shooting sessions. It too makes life a lot easier at a shooting session.
From left to right:
Small powder flask: Good for hunting. easier to carry around than a powder horn. but not ideal for shooting sessions due to capacity.
NOTE: You NEVER pour powder out of a flask directly into a barrel. There could be an ember from a previous shot still there which could result in ignition of your entire bulk powder in the flask/powder horn. ALWAYS pour powder from a measure or premeasured speed loader into a barrel.
Powder measure: This is is graduated by volume (the amount of space a powder charge takes up). set it to your desired charge per the measurements on the adjustable stem. Pour powder from your flask/horn into it and then dump into barrel.
Capper: Shown are three styles. I prefer the middle one which is an inline cappers (two straight ones shown...one for #11 caps and the larger one for musket nipples) vs. the one to the left.
Nipple Wrench: That's the T handled tool 6th from the left. This allows you to remove the nipple to clean it and the flash hole/channel. The top screws off and inside is a small wire attached to the brass top which is also a nipple pick. The tool can hold 1-2 spare nipples depending on what size they are...very handy.
Nipple Pick: The last item on the right made of brass is a dedicated nipple pick to clean out the nipple and possible the flash hole/channel. Since the nipple pick is incorporated in the tool above, if you have that you don't need this one as a stand alone unit.
Small Ram Rod attachments in lower row from left to right:
Ball screw/puller: Needed when you pound a patched ball or conical down the barrel wthout powder under it. You WILL do this!
Plug scrapper for very end of the barrel to scrap crud off inside.
Spare Nipple
Cleaning jag....there are many different types.....including those that spin freely.
Shown here:
Ball bag: Rather than carry around the entire box of round balls that has a tendency to open up, this ball bag made of leather has a slit in it to feed the balls into. The leather tongue folds over to prevent the balls from coming out on their own. Old frontier design that's as handy today as it was back in the 1800's.
Small leather tool bag: Holds the nipple tool and the Ram Rod attachments.
Possibles Bag (which holds all of the stuff shown above and possibly more depending on your needs) and a powder horn.