I have 2 1863 Sharps carbines that I shoot in N-SSA competition. Are they accurate? Well one of the Sharps is my dad's favorite competition carbine. In a novelty event, the targets were 5 ping pong balls and 5 marbles hanging on strings at 25yds. Offhand, he got all 5 ping pong balls and 4 of the marbles with the Sharps. I've seen him hit the twist top on a soda bottle at 50yds with the same gun.
First off- you really, really need to know your bore size. That means slug and measure it. With that in hand, here's the ONLY guy I'd order bullets from-
https://www.lodgewood.com/Bullets_c_7.html
Powder- holy black real thing, no subs. Get the good stuff, Old Eynsford (Goex product) or Swiss. The Sharps has a convoluted flash channel so don't make igniting the powder any harder than it needs to be by using a sub. Pyrodex is also way more corrosive than real black and fouling much harder. Again, don't make this harder than it needs to be.
Caps- RWS or Schutzen only. CCI are garbage and again because of the flash channel shape, you need all the oomph a cap can provide. My Sharps both run great on RWS. I get occasional misfires from Schutzen. The issue there is the shape of the nipple v the shape of the cap. Schutzen are mild steel while RWS are soft brass.
Loading- yes, you can breech seat the bullet and pour in a measured charge and shoot. It won't be the most accurate, but it will work. If you're making cartridges, filler is NOT needed. That's how the Sharps chamber is designed. Start out at about 40g 3fg and work upwards in 3g increments. I'd recommend Charlie's Tubes, it beats the crap out of nitrating paper-
http://hahnmachineworks.com/html/PaperCartridge.html
Lube- lots of recipies, but I've found beeswax/lard 50/50 to work very well in my Sharps.
Keep that falling block and related parts clean and lubed! If you get Charlie's Sharps mod or Larry Flees, you can shoot up to a 100 straight with no issues.
One further word, be careful of Utoob videos. Unless it's somebody I know, or a member of an organization I trust, I would be very leery of what's being said. Often it's somebody after their 15min of fame spouting something somebody told them somewhere, especially if it's from a reenactor.