Back when I was working, D-sized drawings were the norm. Even my microprocessor-based designs fit on them, although most bus lines ended up being combined into a single line for the trip across the page, then fanned out at the ends.
These days, my designs are simpler - they’re for me, and rarely involve anything that complex. 8-1/2 by 11 (A-sized) in my notebook usually works fine. If there’s more than that, break separate functions apart and label the connections between.