Photoshop is not particularly efficient at using many CPU cores. For example, I tried running Photoshop on our primary server we use for building profiles (4X 14-core Xeon, 256 GB memory, 2X Tesla graphics cards). Until file sizes got huge, Photoshop was if anything less responsive than on my XPS 13 laptop with a single Core i7.
More than 6 cores gives diminishing returns for your money. I would budget stuffing your system with memory and a decent-sized, fast NVMe SSD. Add a video card that is capable but not top-end (e.g. Nvidia 1070) if you plan on using GPU accelerated plug-ins such as those from Topaz.
All this assumes you are not working with 100+ MB, full-frame medium format captures. If so, you'll likely want something other than Photoshop for processing RAWs. Beefier systems are in order here.