How can I delete a lightroom folder along with all pictures in the folder to save storage?

Which storage type is close to the limit: cloud storage or local disk storage?

If it's cloud storage that you are trying to deal with, you can use the "Archive" option in the Lightroom Desktop app (right-click on the folder and select the "Archive" option then follow the prompts). The archive option will save a copy of the originals to your local storage, then delete them from the cloud.