I got started in reloading with black powder 12 gauge for a damascus twist shotgun before shotcups were common. You're going to run into a little trouble getting card wads for those brass shells. I understand they need 11 gauge wads because of the thinner walls. Try BPI and Olde Western Scrounger for 11 gauge over powder wads. You might wind up having to make a circle punch to cut your own OP wads. Book covers work well for this. If filler wads are a problem, hardwood sawdust mixed with about 10% mineral oil works. Just make up a dipper that throws enough sawdust to be compressed pretty good when your slug is seated. 60 grains of Fg is a reasonable charge.
Your best bet for a slug is a simple round ball the diameter of your choke. Dixie Gun Works will make you a mould to your specs for about $30. There's Brit feller who makes nicer ones
http://www.jt-bullet-moulds.co.uk/moulds.html for $35. The RB is in period, the easiest to get to shoot well out to about 50 yards, and the cheapest. You can keep leading down and help keep the ball in place by pouring a little melted beeswax on top of each ball after the shell is loaded.