A friend's dad stopped out and helped me today, feel like I'm ready to rock n roll now. What do you guys think? See any issues?
No not really its a 2x14 now with the extra stud and you have just additional support with having 2 support studs on each side. Just make sure the door fits because you have an altered non-standard door size now though, that would be the only issue if there was one.
I would never use OSB for anything, I would only use real plywood especially since it can get wet, dry, get wet, dry with no issues at all. I would 100% do real 5/8 plywood on the roof(calculate snowload) and do tar paper and the tin roof over that. I had a tree come through my house, if there was no plywood it would have been far far worse and likely would have messed up way way more than it did. Your life is worth the cost of the plywood(not OSB garbage). If you use screws make sure your rubber gasket is not broken or you will get leaks.
For the insulation, you need to do some calculation on airflow through your walls, because that will determine a nice dry inside vs a stuffy, never right, damp inside. I would never use a vapor barrier anywhere in the USA, you don't need them and don't let somebody trick you. I recommend sheeps wool for the insulation, its the hands down best functional, rating, everything.