Q: Space mgmt on Macbook Air 13"

Thank you for your reply.  I have been using OmniDiskSweeper because it was recommended by someone in this community on another post for the same issue.  It is a great tool to identify which files are taking up the most space.  I'm having trouble figuring out which files can be deleted and locating the files to delete them.  For example... iLife Asset Management is taking up 5 GB of space but the folder is hidden.  From my research, it appears that I can delete this folder and it won't do harm to my images. 

Good point about the backing everything up.  I regularly back up to Time Machine.  Would this be sufficient?

Also I'm doing the math and the storage space that the OmniDiskSweeper is showing me doesn't match the amount of storage that my mac is showing.

I rebuilt the Spotlight index but nothing has changed.  I do see that the applications I am using for editing my images is taking up a lot of space. 

The catalogs for Lightroom, updates, previews, etc takes up a lot of space.  I am sure I can clean up some of that but I have to be careful because I don't want to lose my images.  All my images are stored on the external hard drive.

I also see that my mobile back ups are stored on the computer.  I assumed that was stored online in my cloud.  I have 50 GB of iCloud space that I pay for each month so I can keep this stuff off of my hard drive.  I really need to the space on the hard drive to keep my image editing software working efficiently. 

I ran the Daisy Disk as recommended by someone at the Genius Bar.  It shows that I have 39.6 GB of hidden space.  Something is wrong.  That is a lot of hidden space.  The hidden space is not showing up in the OmniDiskSweeper and that is why it doesn't make any sense to me.  This is the missing information but what do I do with it now?