Going to jump into the debate, Active racer here, short lines make a HUGE difference, you lose some low end due to the power strokes being smaller but in general they really slow the kite down which helps hugely allowing you to hold a bigger kite for longer. No more getting lofted off during tacks. ...
How can Spotz can be expected to cover impact on their warranty? Foils are engineered to hold people up and go fast, not hit things!
I think they have excellent service, my mast was sent defective and they sent another straight away
12m foil kite. I'm the same weight as you and have used as early as 6 knots (true recorded) , 15 knots starts to feel overpowered and 20 knots is pure survival. so 8-13 would be perfect.
6 knots is foil kite territory, I've foiled around a top mark which had a recorded 4 knots with a 12m chrono (70kgs) but that was absolute minimum, bareeeely foiling. would suggest a 15m+ foil kite.