Boot drive changes on Windows 10 Pro machine to Smaller SSD & Point my Docs to

Hi, Good Morning
We are working as an administrator in the IT Department.

First of all, We are embarrassingly not all that good with EUFI boot stuff. We are still in the BIOS days. (seems simpler?). And then with the secure boot?

whenever we have to get a EUFI machine to boot off a thumb drive, we turn off secure boot? And or enable legacy? we just keep trying things we got a new Dell Windows 10 pro mini tower with 500GB hard drive (and, what, something like 3 - 4 partitions not including the C drive.

The others are recovery, etc?) for a neighbor.
we thought we would help him out / give him a better experience - we want to clone/move the C drive to an SSD (128GB) for faster boot and then use the HD for storing my docs/desktop, etc.

For the cloning - we tried a Clonezilla (likely a version from within the last year) that we have on a USB drive and chose proportional partitions. Would up getting an error during clone about being unsuccessful. That was a week ago / we forgot the error message. we have to get this to them in the next few days so we have to get moving on this : )

Any tips/advice on what app to use to clone to a smaller hard drive, how to make the bootable USB, what settings to choose? Leave EUFI turned on? Secure boot On? Off we when booting from USB only? always?)
And for moving my docs/desktop / as much of other things - temp? as we can to what will be the d drive.

we know you can right-click on my docs and choose change location. we don’t want to break things to try it… but does that make the move transparent to the user? (do they still go to c:\users\user\my docs? and it’s going to d drive our docs? is there a chance they can get around that accidentally and be able to fill up the c drive?

And the temp, our pics, desktop, etc… and maybe even c:\windows\windows\softwaredistrubution\download (windows updates get downloaded to here, right?), the downloads folder, etc.

is there an app to change all those? Some unchangeable? Manually look in the registry for each one?

Thanks!!