Reduce size of Originals folder for travelling

It sounds like you have a well-thought-out plan for managing your Lightroom CC library while traveling. Your approach of temporarily moving older Originals to another drive and then reintegrating them upon your return seems feasible, but there are a few potential pitfalls to consider:

1. File Management: Be meticulous about managing your files during the transfer process to avoid accidental loss or corruption. Make sure to accurately duplicate the folder tree and files on the new drive, and carefully handle the copying and moving of files back and forth.

2. Metadata and Edits: Lightroom CC relies on its catalog file (usually in the form of a SQLite database) to keep track of metadata, edits, and the location of Originals. Moving files around outside of Lightroom can sometimes result in metadata inconsistencies or lost edits. It's crucial to ensure that Lightroom's catalog file remains intact and accurately reflects the changes you make to the file structure.

3. Synchronization: Upon reintegrating the previously deleted Originals back into your Lightroom CC library, there might be some synchronization issues, especially if edits were made to those files while they were temporarily removed. Lightroom may need some time to reconcile the changes and update its catalog accordingly.

4. Backup: Always have a reliable backup of your Lightroom catalog file and your Originals in case anything goes wrong during the process. This ensures that you can recover your data in the event of accidental loss or corruption.

When using Lightroom (not Lightroom Classic), all your photos are consistently stored in the cloud. While local copies are not necessarily required for active usage, they can enhance the speed of your workflow and allow you to work offline without an internet connection.

You have 5TB of local original images? That, and what you ask us, sounds like you are probably using Lightroom Classic (or its predecessor). 'Lightroom CC' is an old name that was abandoned years ago. If you are indeed using Lightroom Classic, then what you want to do will work, but is unnecessarily complicated. Lightroom Classic can store originals on any drive you like, also on multiple drives. So just move the old images to the other drive and let Lightroom Classic manage them there. No need to move them back after you've returned from your trip.

If you are using Lightroom (cloud) after all, then just delete those originals. They are not needed. I doubt that removing them and putting them back on return will work.

You have local copies only of the originals, right?

If you work with Lightroom (not Lightroom Classic), then all your photos are always in the cloud. The local copies are not actively needed, though can speed up work and work w/o internet access.

Let me know if I got you wrong.