As for brands, I mostly wear First Lite. Great for tall people like me. I also love Stone Glacier, which can fit tall folks well, and is local to Montana. All of the major brands seem to be good quality, so you have a lot of good choices.
A full layering system is important. If i walk 20 meters i will be sweating in a 150g long sleeved shirt when it's below freezing. Stop for 10 minutes and I need two more layers to keep warm. Too many variables in weather, exertion, and body type to pick one outfit. Get a whole layering...
If you hunt long enough, you'll lose an animal. My son lost the first deer he shot with a bow. Good lung shot, but we were too excited and pushed in too soon and jumped the buck, never to be seen again. I think your approach is correct. Evaluate what went wrong, determine what you can do...
Killed a nice mule deer this year. 420 yards with 6.5 PRC 143 ELD-X. Total passthrough. Heart and lung, but no bone. Still managed to walk about 10 yards, but no big deal. I agree with many that neck and shoulder shots seems to be what drops them in their tracks..