My two bits would be to definitely go with the vest first. In my experience apparel is much more complicated than tarps, stuff sacks, packs etc. When you get into fiting collars into neck holes and sleeves into arm holes, small differences in seam margins end up with things not fitting correctly. The vest will be much more forgiving and a lot less frustrating than the jacket. I should say that I have not made the jacket, but have looked at the instructions and would personally rank it as a very advanced MYOG project, not saying you can't pull it off, but I think you would have less frustration and a cleaner finished project if you did the vest and then applied what you learn to the jacket.