The frame structure for the cockpit area is framed up with 1/8 balsa, then when the clear windows were in, I overlaid those with 1/64 ply. The top, of course, is carved from a block and then hollowed extensively. I didn't/don't worry about strength much in a spot like that, as long as it's vibration resistant I'm happy.
I never draw my ships out except for maybe an outline sometimes. I just start tossing stuff together and hope for the best. seems to work for me, maybe not for others.
You're right, the Pawnee is a good plane to fly as long as you are willing to accept the couple of shortcomings it has. The vertical tail is very anemic and any direct crosswind above 15 knots is work. Of course, by then you've quit spraying anyway if you're knocking down "hot stuff'. (At least around here.) Plus, it really is a small airplane for the flat farms in northwest Ohio - some fields here are two to three tank fields with a Pawnee's 150 gallon tank. If it's hot, that drops fast. Foliar feed is very heavy and that was a super busy job for me, but the stuff is very heavy for the amount of gallons per acre and the Pawnee takes some nasty slow application speeds to get it done. But... still a good starter ship for a new operation.