Answer to your 1st question= yes as long as you are using a conversion cylinder, I would not recommend using smokeless powder when using the cap and ball cylinder
#2- for reloading it is easier to use 1 caliber, less changing of the dies and powder measure, I often shoot different calibers during matches. 38 special for pistol and 45 colt rifle. I sometimes use my 45 pistols and use Schofield ammo, or run 38 LC in my open tops. Mostly black powder but during summer smokeless.
Last question- run what you want as long as you are safe and having fun.
Welcome
Rafe