R12NV,
I can't give a definitive answer as to the maximum number, but can give an example of my own experience. At present, I have a project going with over 30 separate layouts (as opposed to viewports) and have each setup to go to their own independent plotting devices (2 different plotters with multiple sheet sizes). Each layout is uniquely named relative to its use and when I'm ready to plot them all, I select all tabs at once, right-click and select plot. Very convenient.
Hope this helps. Jeff Foster, PE
CE Group, Inc.
Apex, NC