@Christina Hi I am not sure as I brought a ready assembled brand new workstation direct from HP. A base specification defined from this with all these options
The workstation did not have a graphics card so I did not waste money on one I did not need then added a 1080TI and a GT610 purely for graphics.
I only had a single cpu E5 2620 v4, has 8 cores/16 threads but you can add another later. It came with only 16GB of ram but can be extended to 128GB per cpu, max 256GB, can only use ddr4 registered dimms. Has PCI 3. Is future proofed.
The second cpu is a module that includes a further 4 memory slots, I am not sure if thats available with older cpu’s. But I am not an expert.
Make sure you find out which version the cpu is ; the E5 2620 v3 is 4 cores /8 threads and supports ddr3 . You can always google “E5 2670” to get the
I know in the UK there lots of flavours of used Z600 and Z800 workstations on eBay, which I guess have come to the end of there commercial live. I looked at these and thought in the long run getting new would save me being again next year plus I now have a 3year warranty.
Anything else don’t hesitate