Can I delete my documents once i made a backup

If I got you well, yes you can backup your iPhone on the cloud and the backup will contains all the data (but be aware that you won't be able to restore the single file but only the entire backup).

With the Mac, the best option is to enable the iCloud storage and then enable the storage optimization so the Mac will automatically move in the cloud only the stuff you use less.

Have a look here to more info:

How to free up storage space on your Mac - Apple Support

How to back up your iPhone, iPad, and iPod touch - Apple Support

About backups for iOS devices - Apple Support

Are you asking about doing a backup or syncing?

If syncing, iCloud is a syncing system, not an external storage system. If you delete them from the device/computer they will be deleted from iCloud. For the computer, go to Photos/Preferences/iCloud and select Optimize. That will reduce the space required by about 90% when fully effective. To increase space available a device, go Settings/Your Name/iCloud/Photos and select Optimize iPhone/iPad Storage. That will reduce the space required by about 90% when fully effective.