SCENARIO
88 x iPad Air (1 grade level)
each with an average of ~10 to 12GB usage
use single iCloud account with 1TB space for backup
every single app has license for each device (via VPP spreadsheet)
we configure 88 devices with same iTunes/iCloud account so that we don't need to push newly purchased app thru MDM. new apps automagically appear via "auto download" feature of iTunes Store
BACKGROUND:
We used to configure each iPad with their individual iCloud account, but the free 5GB is not cutting it. Most of the iPads keeps displaying a pesky warning that iCloud has ran out space.
Question:
For iCloud backup, is there a documented hard limit to the max number of devices you are allowed to associate with a single iCloud account? or the limit would simply be the available iCloud space?
Is there a better way?

