Robert: Now that I have the Funky built,I think it is a very good kit in most respects,but there are some quirks,and terrible instructions.
Regarding the spars: as the wing is flat,no dihedral, I just centered all the spars in the middle of the wing,thus requiring splices a few inches from the tips. Therefore no problem re strength. BUT<do not waste any wood of any size. It may not seem like it,but there was enough wood for the spars and the rest if planned properly.

The wing is built upside down,and it took awhile to be certain of that.Also the piece in the center of the wing that holds the dowels was a bit confusing re which side up. Had to go to their instructions on their website and check their pictures for that and a couple other things.

I also have a sheet of [1/32nd?] left over,and a small piece of maybe quarter inch sheet,that I have no inkling of what they are for.
I did not appear to have the pieces that run under the canopy between the two formers.

1/4 sq.stock is very near 6mm. Hope this helps. Dave