Probably around 1/8 x 3/8 for the LE and 3/16 sq. for the TE. A dozen years ago (about) someone in the LA area shrank two of JAck Sheeks I-Beam designs to ½A size; they almost looked like jewelry! One was the Beech Staggerwing. He covered with transparent Monokote so the 2,458 little riblets were visible! I don't remember which of the monoplane designs he did. (I guess I was too imppressed with the Beech.)

Remember that, even more than with larger planes, weight is the enemy, and all those little pieces have to be stuck together with something. You might consider thinned Elmer's appl;ied with an artist's brush, which will be adequate if the pieces fit with precision.

I have plans for the Beech tacked to a door in my shop. Someday . . .

When I built my IBTW Barnstormer I had reduced the Baby Barnstormer plans to 75%.  Then I built it replacing the 1/16 sides , doublers and ribs with 1/20 sheet.  The plans call for 1/20 sheet wing LE and I used 1/32 sheet.  I also used 1/8 square for all four spars and the leading edge.
Clancy