I recently just went from ski to snowboard.
Its a total different feeling, i would suggest a forward stance with your binding since you are used to facing down the mountain and it will be easier for you to learn and get the confidence. Then transition into duck if you are not doing one direction. Falling is a lot worse and more painful in snowboarding since it harder to fall the way you want too. So just keep it going, took me a whole day to finally learn how to link turns and not eat it every 5 feet lol.
Im also 6'6 220 and my boot size is 15 lol, so if i know one thing its that im more built for ski but as a Marine i never accept defeat haha