I am new to leather work as well, but I can make one recommendation that has really helped me to get started. T.C. Albert's book "Recreating the 18th Century Hunting Pouch" is the next best thing to having your own personal instructor. He shows the basic tools he uses, the text and pictures are spot on - no filler. It has a nice little pictorial section on historic bags and full size templates you can use and modify to make a few different pouches. OBTW, a section of the step-by-step instructions includes how to 'age' a pouch as well.
More to the point of your question, he starts out by talking about the type and weight of leather (his preference is veg tanned and 3-4oz or 4-5oz which is a little harder to work).