The PHRF requirement is a bit of a strange one if trying to build a large spectacle race? And Its not clear yet what the $100 to $150 entry covers, but if its just the race, might be a bit steep for some.
i dont want to sound negative, the concept looks great fun.
cut the holes oversize with rebate and install/glue solid timber (kauri or the like) "picture frames" with the actual rebates for the windows. You want to remove any chance of water getting into the plywood's end grain