That seems like a lot of 36" and 24" cables, but it’s really contingent on if you’re arranging the instruments vertically or horizontally.
I arranged mine vertically and I never bought anything above 24" according to old Mouser receipts; I don’t think I ever ran into a situation where that came up short.
Also, keep in mind that you will be self-patching each instrument a lot, especially PB; the PB2 is 16- 1/2" x 9-1/4" according to a MW post (sounds right), so corner-to-corner is ~19"; that’d be a lot of slack if you run out of 12" cables (which you probably would).
Sorry, I don’t really have the right number for you, but that definitely sounds off to me.