Do you plan to load with black powder or nitro-for-black? This will make a big difference as to how you construct your loads, with specific wadding needed in each type of load. I am not experienced in loading black powder, but I know that Paul Matthews has a lot of information about what wads and grease cookies to use.
I believe your bullet diameter should be set in relation to the bore diameter just ahead of the chambers. I would go for a bullet that is bore diameter, so .450" from what you said. You then will try various types and thicknesses of paper for your patch, beginning with lighter papers and working to heavier papers until you get a good seal and see no evidence of gas blow-by when examining your patch fragments.
Another sign of gas blow-by will be some leading in the barrels. Once you get a good seal you will experience no more leading. It's not really difficult.
Several years ago I wrote and self-published a little article that many have found useful:
http://rbsiii.com/PaperPatchedBullets/index.htmlMaybe it will be helpful to you.
Good luck!
Curl