For CPU and video card selection for use with NinjaTrader, it is important to understand how NinjaTrader works. NinjaTrader_Jim says: "NinjaTrader has multiple threads for different tasks. To keep things simple, there are UI threads, there are Instrument threads, and there are thread pools. Rendering and GUI work happens on UI threads. Processing data happens on Instrument threads or in thread pools for historical processing. Instrument processing must be synchronous for NinjaScripts to function properly. This means that resource intensive scripts, like volume profiles, cannot distribute their work among multiple threads. In the application, all of these threads have jobs and some of them need to wait on one another. You very rarely will see 100% utilization on an individual thread when rendering lag symptoms arise." NinjaTrader_ChelseaB adds: "The higher the single threaded performance, the better any CPU core will be able handle a larger load. More CPU cores can help offset other work for other threads, so having more cores can help, up to the limit of the single threaded performance for any one thread on any one core." So, get a CPU with a number of physical cores equal to or greater than the number of instruments in the workspace, and with the highest single-core GHz clock speed you can get. Get at least 32 GB system memory, and a graphics card with high computational performance (see here). So if you are running NinjaTrader 8 with, say, around 16 tracked symbols, and workspaces with complex scripts or many scripts and drawings or multiple workspaces, or may do any of that in the future, no question about it, upgrade to AMD Ryzen 9 7950X. It's 16 core, 32 thread, at 4.5 - 5.7 GHz, and AMD Socket AM5. Compare it to your existing or other CPU options at CPUBenchmark. Right now it's the best combination of multi-core and single-thread performance for NinjaTrader, and at a great price. To upgrade all components will be over $1,000, but that should be the least consideration for an essential work tool.
Improve your networking also with network card- software-driver with an automatic roll over from hardwire to (wifi to cellular hotspot). Plus you get a better build quality, imo. I have numerous friends with lower end stuff that dies after 12-18 months, but not before being unreliable for an extended period.
You don't have the free choice of parts. The mobo dictates. That is, it will not run "just any CPU you want", but will have specs as to which models it will run. Also the max model of RAM and RAM speed will be determined by the mobo. Personally, I like workstations... for lots of reasons. I'd suggest you look into them (Dell, HP, or Lenovo). You'll get quality and save a lot of headaches. If you want a rig that specs high performance, get a gamer rig with hot Ryzen CPU.
I have two computers but I do on purpose not put them in a network. I don't want that one computer can infect the other one. One computer is only for trading, the second one for all the rest (surfing, emails, excel and all the rest). I also only use internet by cable, never wifi. All computers have vpn (so also the computer from my wife/children).
Just to be clear, the Wifi-cell is for hardline failure roll over backup only. It actually works pretty good for me, such that in about 4-5 seconds I am reconnected. For sure a poor mans solution, but at least it does work, is testable on a regular basis.
People are different. While you're rational, I'm not that rational. I got myself a Ryzen 5600 but it's way more than I need for trading purposes. I've psychologically disconnected myself from trading profits/losses and life expenses.
The only problem that I still have when buying a new PC is the fact that I cannot find anywhere a list with graphic cards that also shows the maximum resolution they can handle. For instance: if I have 2 screens that I want to connect to that graphic card, I need to know which cards can handle the resolutions from these screens. 34 inch screens I use have 3440x1440 resolution in format 21:9. So how can I find out which graphic cards I can/should use?