8GB should honestly be plenty, id say get the ultrasharp, keep the ram at 8… do your thing and see how much memory usage your pc is actually using, unless your editing video, photos and haev multiple instances of everything up 8 should probably do the trick…
If its not, get more memory and put it in
And usually you can add another drive or two
If i was dealing with a fuckton of photos and videos, id setup a nas or something of the sorts like Ilya suggested, would allow you to acess them from anywhere on the network, or from another computer/location if you so choose to allow the ability to do so. Also look at getting something like Carbonite, always have multiple backups of anything thats precious to you.