There are a lot of BPCR shooters who claim the Large Pistol primer produces a more accurate and consistent load. You should be just fine using the large pistol primers with black powder. I am sure some where in an old post you stated the length of your barrel, if over 30 inches additional lube may be required. I do get much better results in my 32 inch barreled sharps with the addition of a lube cookie as the bullets I have been using run out of lube in the longer barrel. This is not a problem in the 26 inch barreled rolling block I acquired.
Although the large pistol primers are pretty much proven for use with BP, I would not use the large pistols with smokeless, they could be just fine at trapdoor level loads but why take the chance.
Somewhere around 65 grains FFg should work. Swiss is supposed to be pretty good stuff.
Some folks even put a single layer of tissue or some other paper over the primer to moderate the primer flash. I have not tried that yet.
There is lots of info on the BPCR forum
http://www.bpcr.net/forum/viewforum.php?f=34