Curious how long you actually waited in that staffed line before you decided it was worth it? I've done the same thing but always wonder if I'm just being stubborn.

Screws every 8 inches sounds like a lot to me, no offense. In my experience glue does most of the work on a ply box and the screws are just there to hold it tight while the glue sets, so a few well placed ones per joint go a long way. The part that actually bit you in Toledo was probably the nails, since brads have almost no pull out strength and glue alone on end grain ply is weak. Your mileage may vary but I'd say 2 screws per joint plus glue, and make sure the box is square before you drive them. The cast iron thing would've wrecked most lowers anyway, so I wouldn't rebuild your whole method around one heavy load.

Who hasn't been that guy doing mental math on a $14 plate of nachos while everyone else just wants to eat? I'm usually the cheap one in the group, so I feel this in my soul. One time I caught myself counting chips like a total weirdo and had to stop and ask what I was even doing with my life. Splitting by head count only works if everyone eats the same amount, and nobody ever does. The real move is order more than enough and just split it even, then nobody has to play accountant. It costs you a couple bucks at most and saves you a friendship.