Hi LordoftheSith327,
I am Dave, I will help you with this.
1
Disk Clean-up Does not affect your personal files, you are correct in your understanding, it deletes old System files, temp files and installer files for Windows updates that can be safely removes and no longer needed
2
Defragment and Optimize:
This will also not affect your files, basically on HDD's that moves all folder back into neater groups because files can be stored in bits around the drive and it puts the back into a neater storage that will make it more efficient to access the files and puts all the dree space into one location on the disk
You should never defragment an SSD, that uses a different technology named TRIM, that is enabled by default and optimization will happen automatically on the drive.