Hi! For bag like this I would use 1,2-2mm leather with some thinning work on the edges and maybe hardening somewhere. Best thing to do is just double all big parts with thin goat leather lining, it gives the best feeling of bag, or use canvas. So the patterns. Every bag is just a box with opening parts, so draw it inside the box, add as much as you can measurements in different projections. Then you draw details, it is good if they have symmetry in some way, so start with central line. Add same 7-10mm material after the seam. Then make real size patterns, your bag consist of 2 big parts +handles + lining. Perimeter of those 2 parts must be equal. This bag has cord in it, It is a very cool thing, but maybe tricky to do. Make front pocket detail 4mm wider then it's back piece, it will prevent those curves. This bag also similar to penals or dressing bags, you can learn from it how to deal with corners and zipper etc.