moving large files to ssd on dock (Mac Mini M1)

[Sai22]

I have just acquired a Mac Mini M1 2020 8GB RAM, 256GB SSD

After restoring my stuff from Time Machine I am left with hardly any space and have ordered a dock which has a SSD slot.

My question is, what folders can I move to the external drive (SSD, not sure how big yet)? I would like to store photos and iMovie projects there, but I was wondering if I can simply move the whole library file from the start up disk to the new external drive, or will that just mess stuff up? (I do have a bit of a history of trying stuff out that I don't really understand and creating worse problems).
Thing is, in the library folder, there are a load of folders, which I have no idea what their purpose is, but I think they must have some function. If I change the location will that mess something up too? Better to just create the photos file and the iMovies file on the new external?
Thanks for any advice you may have.

 

[arw]

In general, you can move surprisingly much to external disks.
For Photos you can simply move the whole "Photos Library.photoslibrary" to the external SSD and then start the Photos.app while holding the "alt" key. Photos then asks you to select a library and you can navigate to the external SSD.
It seems to be similar for iMovie.

Move your iMovie for Mac library - Apple Support

To save space on your Mac, you can move your iMovie library to an external storage device.

support.apple.com

In regard to what folders you can move: Although possible, I’d avoid moving applications themselves or your home folder to external and stick with the applications library files.

 

[Sai22]

In general, you can move surprisingly much to external disks.
For Photos you can simply move the whole "Photos Library.photoslibrary" to the external SSD and then start the Photos.app while holding the "alt" key. Photos then asks you to select a library and you can navigate to the external SSD.
It seems to be similar for iMovie.

Move your iMovie for Mac library - Apple Support

To save space on your Mac, you can move your iMovie library to an external storage device.

support.apple.com

In regard to what folders you can move: Although possible, I’d avoid moving applications themselves or your home folder to external and stick with the applications library files.

Thank you sir