Ron - yeah, it takes quite a bit of cord.   I was thinking I could complete both chairs with a single spool (approx. 1800 ft), but after completing the first backrest I realized I have to order another spool.   Today, I finished weaving one seat, and it took 3.46lbs, so not quite as much as the backrest, but still over 600ft.

Ty - Thanks!  The only reason I knew how to weave the backrest like the CH25 is from a two-part article by Caleb James in Popular Woodworking June/August 2017.   It was extremely helpful.