How much iCloud storage do I need?

See the following two articles for details on device and iCloud storage usage:

About storage on your device and in iCloud - Apple Support

Manage your iCloud storage - Apple Support

Or if you're presently not in a position to reduce your requirements, consider purchasing the next higher increment of iCloud storage available.

If you have a local Mac or Windows system, you can also back up to that as an alternative to using iCloud.

You are welcome. Another option to free up space is to delete some prior backups. That turns backups off, so you will need to turn them on again.

Manage your iCloud storage

~256 GB of data isn't going to fit in a 5 GB plan. Not unless almost all of that is music or apps that you've directly downloaded from Apple, and can be re-downloaded without needing backup. If your iPad is middling to moderately occupied and any appreciable portion of your iPad data contents are your own documents or presentations or app data or your own music or photos or videos, that's just not going to fit into 5 GB.

How much iCloud Storage you need depends on the amount of data you want to sync with iCloud. For example, if you have 15 GB of photos, but decide not to sync them to iCloud, you won't need that space.

If you upgrade to the next level, you should have plenty of space.

Buy more iCloud storage

You are welcome.