Zachary, congratulations on making the prettiest sail model ever!
The Roscoff junket really was an awesome event, as you say the friendliness and encouragement were inspiring.
I am thrilled that you are making a Reddish Rig, it makes a lot of sense on a heavy old bilge keeled Westerly that is never going to win races to windward whatever the rig. Speedwell of Hong Kong is one of my favourite boats and proves the rig beyond doubt.
I'm not sure if your model is big enough to demonstrate how a flat-cut fanned sail develops camber when you induce twist in the sail. When I built a larger model (of a higher aspect ratio Reddish-type fan) it was a real epiphany to view the phenomenon. At risk of inducing the wrath of junkies who have been developing the many and varied cambered panels, I often think that many of the older ideas have a lot of merit and may have fallen out of fashion for any number of reasons, not just performance.
We'll be sitting at the drawing board tomorrow and deciding between the higher aspect ratio Reddish rig or a fanned Gunter-Junkette (watch this space...) on the existing mast on our Westerly 22.
As far as sailmaking is concerned I'd suggest following PJR and trusting your own instinct along with any direct answers you can glean on here. For example your lacing chafe concern would probably only become an issue half way across the Atlantic, it just might not be a problem for you.
In Roscoff I was impressed by Fly's sails and the battens laced on with cable-ties through two eyelets. Lacing on battens by whatever method rather than using batten pockets will give you more leeway in experimenting with different sized battens or possibly hinged battens in the future.
You must have read this too?:
https://www.junkrigassociation.org/Resources/Documents/Merits%20of%20Flat-Cut%20Junk%20Rig%20Sails_web.pdf
Please do keep delivering updates.
Some rushed photos of my model. The dark embroidery thread leading horizontally back from the luff at the third batten shows six to seven percent camber about half way along.