Don, the best thing you can do at this point, is be consistent! Keep notes from start to finish!
A jig is only good for repetive length and tapering... Period! You can do the same with 2 nails or pegs. Stagger the strands and begin your loops! There are many ways to skin this cat!
If you read thru the posts, alot of different lengths are mentioned!
You seem to know the foundation, construction principles, to building a flemish style. The material used, will also dictate measurements used.
Smaller diameter materials and low stretch, creep, will mix the recipe, also!
I would say, stay with one material, consistent on measurements, and keep record. If you come out too long, take the string apart, and shorten, say an inch or so. Then twist again, using same measurement for the loop! No need to buy more material!
It amazes me that someone would would use, similar pieces of wood, to build a bow, but use disimilar materials to make the string?
The arrow is, I believe, the deciding factor!