26 layers of 6 ounce in a hand layup works well for FCS and futures boxes, which are 0.25 inches wide on the flange.
36 layers of 6 ounce for the normal single fin center boxes, which have a 0.375 inch width.
It's best to orient your fin template so the fiberglass yarns run from the base to the tip on an angle for the best flex. Having them run straight parallel and perpendicular to the base makes for a floppy fin. So make your fin panel big enough.
I think you'll need somewhere around 60 oz of resin to make a 36 layer panel...