There is no single optimal number. A lot had to do with what you have.
If using 32mm hole spacing I'm starting with this formula to figure out what you need... assumes a hole spacing under the top and the bottom most hole is used for the first shelf, maybe Yu could do the top differently...
Number of holes needed = [# of sys1 * 5] + [# of sys2 * 7] + [# of sys 3 * 8] + [# of sys4 * 12] + [# of sys5 * 15]
Total height = number of holes * 32
Cabinet height = [total height + # of cabinets you want * 32] / # of cabinets you want
Last formula adds 32 for space below first hole, but I'm not sure if it breaks a sys in pieces.... hmmm need someone's help here to make this work. Also need to figure out to ensure cabinet height is limited to 32mm increments...
So for me:
Number of holes needed = [12 of sys1 * 5] + [11 of sys2 * 7] + [9 of sys 3 * 8] + [11 of sys4 * 12] + [2 of sys5 * 15] = 60 + 77 + 72 + 132 + 30 = 371 [dont judge me]
Total height = number of holes * 32 = 371 * 11,872
Cabinet height = [11872 + 6 * 32] / 6 = ~2010 each, but probably 2016 each to stay at 32mm increments.... and I'd build 7 to give me room for expansion
and so I don't need to optimize it perfectly.
If I want to base it on 2400mm panels, 5 would be 6mm too few, so I would build 6 and most of one would be empty. I just think 2400 is a bit tall for drawer systems.
Help? Suggestions to improve?