1:32 twist is a bit fast for patched roundball (PRB), but many make it work. Most report that a lower powder charge is necessary to get decent accuracy with PRB in a higher than ideal twist rate. To be clear, 1:66 to 1:60 is common for a PRB preferred barrel twist. 1:48 is considered a "combo" twist rate of sorts, meaning it'll shoot both PRB and conical decent. Faster than that is generally more dedicated to conicals/bullets. But again, many have found that PRB accuracy can be acceptable with faster twist rates like yours, but definitely start at a lower powder charge and work up.
Hornady Great Plains Bullets shoot really well in my 1:48 twist, I'd think they'll shoot really well in your 1:32 as well. They do tend to lead up the barrel. Someone else recommended cleaning the bore with a bit of steelwool, make sure it is "0000" size so it doesn't mar the bore.
Real black powder, Triple7, Pyrodex are going to be needed to ignite well in your caplock. BH209 would require 209 type shotshell ignition. If you have trouble igniting Triple7 or Pyrodex, there are #11 "mag" caps that are a little hotter or Musket caps would be a bit hotter than regular #11 caps. Also, many say that a nipple that has around a .031" opening on the bottom will help with reliable ignition with subs. Be aware that shooting heavy loads with heavy conicals will wear out nipples a lot faster than shooting PRB. If groups suddenly open up and/or your hammer starts getting blown back into the half-**** or full position, time for a new nipple.
I would start around 70 grains by volume and work up in 5 grain increments, not exceeding the 90 grains max charge. That 90 grains max charge is with 2f type powder granulation ("rifle"), reduce by another 12% or so for 3f granulation ("pistol"). 3f is finer granulation and thus burns quicker, creating more pressure.
When swabbing between shots, always pop a cap after swabbing and before loading the next charge. Swabbing may push fouling down the bore ahead of the patch & jag and block your flame channel. Popping a cap will usually clear it again. Point the barrel at a leaf or dry patch when you pop the cap, if the channel is clear it'll make the leaf/patch move.
Look up the bucket of soapy water cleaning method. It works well to remove BP fouling. The most important part is getting the bore dry again. WD40, 91% alcohol, denatured alcohol assist in removing water. Make sure to pour some through the flame channel. Many like to heat the water up so it will evaporate and dry faster, but it isn't necessary as far as cleaning well, just convenient. If using a petroleum based rust inhibitor, many like to store the rifle barrel down so it doesn't collect in the flame channel and cause ignition problems. When ready to go shooting again, strip the rust preventative back out of the bore first by swabbing with alcohol. I like to use Barricade, it only takes a light coating and it dries into a protective film, does not remain a liquid. It also won't cause a mess if you don't strip it out before shooting again.
