I want to play videos, music, view pictures from the SSD. Not add them onto the PI hard drive as there is too much data for my Micro SD card to hold. As an alternative can I have my Pi boot LibreElec if it is installed on the SSD itself? (I so far cannot play my videos without them being copied to the SD card)
As far as I know, You should be able to boot LibreElec from an SSD and store movies on the SSD at the same time. I have never used LinreElec, but I am actualy using a system, that I am typing this on, that is a Pi 3 and a 1 TB HDD in a Insignia External HDD and it runs realy well.
Two things that you need to know is that the Pi 3 needs to be set-up to boot from a USB device, as it isn't doesn't do it out of the box (unless that has changed in the past 6 months).The tutorial that raspberrypi.org has in, I think, voulme #59 is a little too complicated. I went through troubleshooting the whole process here on raspberrypi.stackexchange.com so if you find it, you will find a more simple way to do it.
Also, if you want to move the movies to the SSD from your PC, in my opinion, it would be easiest to do it by plugging it into the PC and copy to the correct folder on that SSD. Be sure though, if you are going to use a PC with Windows, that you do not format any of the partions on that SSD or bad things will happen. Windows doesn't like certain partition formats, and will want you to format them. Don't do it! Ignore them completly.