I can't add much to the advice already given.
I was not aware of using cotton to rub the edges of the leather to slick them down.
I use a light coating of Gum Tragacanth (obtainable from Tandy Leather Factory) and a nylon slicker to burnish the edges of leather items. A resonable substitute would be to dampen the edges slightly with water and use a nylon comb to rub the edge briskly. This should do the trick in a minute or so. Put a piece of light cardboard between the edge of the piece of leather being polished and the rest of the sporran to prevent hitting the body of the sporran with the comb.
If you do use a sporran chain with clip ends, be sure the opening in the chain clasp is away from the kilt. A leather belt is a better alternative, although you need to slick the edges (and smooth the back of the belt if it is rough) to reduce friction.
Hope this helps.

Tom