8GB is probably two stick of 4GB. Their board probably has 4 or 6 slots, so no…that memory won’t work. Meaning, you w’nt be able to fit all of it.
As for the tower, you should be able to install another HDD in there.
I personally would invest in a NAS if you’re planning to do any type of serious work on this machine.
I got a Synology plus a 2TB drive and everything I do on my 2TB PC drive is backed up to my NAS 2TB drive. I’ll eventually add another 2TB to mirror the one already in the NAS (doing wedding photography, you can never be too safe with keeping stuff backed up).
ALSO…as an added benefit of having a NAS…a lot of them can stream media to your TV/XBox, etc. Movies, etc.