My lines are 29 m ; 1 mm diameter for front and 0.8 mm for rear , made of SK99 which I recommend for higher resistance at this diameter ...;
And indeed I have 4 meters "prelines" on the 4 lines , of 1.6 mm each, for abrasion of tangles lines during loops; I do not recall if it is in addition to the 29m or included in the 29m;
I made a bar with 0.6 mm fishing lines, but never tried seriously ... when you have them in hand, you can see that 0.6 mm seems very very sensitive to abrasion on the beach and it is very "cutty" for the fingers ; and I did not found 0.6 mm made in SK 99, so there is IMO a too high difference of breaking load (approx 80 kg) vs 0.8 mm of SK99 (160 kg) and I am afraid to damage the kite in case of break.
I still use the same line set on the video, for 2 years at least, which never broke during a ride (just once , 2 lines cut by my skis, repaired locally by splicing, so the lines are still the same today), even with jumps (soft in those winds).
Illustration of my local repair for 0.8 mm lines