I too have a 'double' barreled tumbler.
I sort brass for comparability, 9s nest in 40s, 44s, 45s and it moves up is sizes, well 44s and all 45s do well together. Bottle necks don't do as well with pistol cases that will cover the case mouth or nest (.223 types slip into 44s and 45s - neither one gets fully clean.).
I punch primers in bottle neck cases.
I fill my drums 2/3 to 3/4 full with brass, then dump in still pins until they stop falling out of site. Add the additives (simply green or Dawn or what ever) and water to fill.
Don't over tighten the screw nut. It will only pull out the stopper cap (it goes on the inside of the drum, so is it a cap?). Let em role.
I rinse with flowing water to wash away the black water, yuck! Check for pins stuck inside the cases and primer pockets. I do this as I shake the cases under water. Then dry. I put mine in a preheated 200 degree oven on an old towel and cookie sheet and shut off the heat. When the oven has cooled, the brass is dry. Other do it in other ways. It all works.
Now, 'how much media?' I don't know. I bought a 10 pound sack and it never wears out.