Hi Adam, Sky SUP 6'3" sounds pretty good for you, if you're willing to also use your board for SUP Foiling. Of course a dedicated Wing Board such as our Sky Wing will feel more compact for winging, but it's not really intended to be good for SUP Foiling, as the short length makes it much harder to paddle in a straight line and catch waves. I personally would go for the 6'3", as you won't outgrow this size as quickly as you would outgrow a 6'7" for winging, which will feel pretty big once you've learned the basics.
For the foil, 75 mast is a good size to learn on and for flatwater winging. Also for most SUP Foil days it will be better to have the mast slightly shorter to avoid hitting the bottom on the small days. If you're mainly foiling in deeper water with chop and swell, then the 82 will be the better option for winging, with the downside that it needs a bit more water depth when SUP foiling. 1750 HA Wing is a good starting point! You'll probably move to a smaller wing with more and more experience, but you'll struggle to take-off with a too small of a front wing in the beginning. 78 FL is good for the start yes!
Hope this helps! Cheers, Klaas