Welcome to the forum and man, they are really testing you. Without spending time on figures, 36,000ft (7 miles) seems nuts to me to try and do that with a single pump. I would be putting lower pressure pumps every mile. Size the individual tank-pumps to get the mile distance+30%. Then size the mile-pumps for the total flow to the next pump.
I think the pipe guy was just being nice by only "scoffing!"