For the texture of leather, I use a dry brush technique and pounce the paint onto the surface with a stiff brush until the paint starts to tack up. I've also used a sponge to apply paint in the same pouncing method. The idea here is to continue pouncing as the paint dries giving you the "leathering" texture you desire.
For the sheen I use a 50/50 mix of water and clear gloss.
