1) What's a good tie construction / fabric for full windsor knots?
2) I'm not a big fan of small knots, but would a 4-in-hand-knot from grenadine ties look bigger than standard ties? I hardly button up the top button from my dress shirts, so I need a bigger knot to obscure the loose button (that's why I prefer the full windsor)
I only tie 4IH, so can't speak to a Windsor. Stitches ties the best half Windsor around, he might weigh in on his construction options. In fact, i was surprised when i learned his knots are HW. But the best method is to email David and begin the dialogue. As his post above shows, he knows how to shape a tie to his customer's liking. Good luck and post pics when you get the tie(s).
Ps, I agree you should get a proper fitting shirt. Ties of this quality deserve a quality frame.