I am considering a new build to replace a laptop that is about 3 years old for processing pictures using Photoshop and related.
 
When building a computer for this purpose, is there specific things that I should place a greater importance on?  
 
I hoping t stay under 1k for a complete build including OS & 20" monitor.  
 
Thanks

Just photo editing work? You won't need anything too intensive... more ram is likely to help the most. With such low power requirements, I'm assuming you won't plan to overclock. An AMD machine with a 780G motherboard is probably the most cost-efficient path for your build.

Yes. More memory. Faster cpu for applying filters, zooming, etc. Faster harddisks like RAID 0.
 
If photography is the only use, you can get away with integrated graphics which have evolved to HDMI/DVI.