That is not good news. I would not buy more storage under the circumstances. I think you need to disassociate with iCloud and iCloud Drive. Look in your iCloud Photos and iDrive folders and see what is there. You will need to make sure everything you want there (i.e., the things not still on your computer) is downloaded to your computer. See how to archive or make copies: https://support.apple.com/en-us/HT204055 You will need to store the downloaded files where iCloud/iDrive can't see them. For example, you might store photos in your Home folder in Pictures. And, you might to store Documents and Desktop items in folders having different names in your Home folder. You also will need to backup the other items from Photos and in Desktop and Documents on your computer in the same way. You could also backup all these backups to an external drive or an alternative cloud. The steps to this point can be tedious. The final step can be scary. Remove the checks in the checkboxes for Photos and iCloud Drive.
Above all let some others reply here on what you should do. I don't want to have missed something, and then have you pay a price. Also, there might be better ways to accomplish what you need to do.