Looks good I would get the 10ga. If you are going to shoot steel you can use modern shot cups to protect the barrels. I would load powder,
overpowder,wad, shotcup,shot then overpowder card. Iuse bismuth out of mine with no shot cup. The bigger bore blackpowder shot guns shoot large shoot alot better than smaller bores.
Just my 2cents others milage may vary.