I would be more than happy to answer your questions, but first I have to ask one. What kind of "paints" will you be applying? I have done a lot of work with acrylics on leather (see my Gold Purse) album recently posted (my first on this site) to see if that is what you are looking for advice on? With acrylics on leather, I have found that getting the paint to soak into the leather is a problem only insofar as it happens all too quickly. Controling drying rates so that one can build rich deep colors is what I consider THE critical issue (at least with acrylics).
In addition to the gallery album, I have attached a couple of other examples for your consideration: