A lot of that will be dictated by your budget. I would start with PC part picker.

General recommendation is that, if you can, get a GPU with 16 gigs of memory and have 32 on the OS. That will help future proof the device so you're not having the same conversation in a few years.

For CPU, amd typically keeps their socket longer than intel. This is your upgrade potential. AM5 is the latest AMD socket. You can be guaranteed at least a couple more releases of CPUs on that socket over the next few years to upgrade to.

The downside is that PC parts are very expensive right now. That's why the gabecube isn't out. So if you're budget constrained, use PC part picker to balance your options.

Apologies for the late reply. I'm not sure I can be very specific for you but here are a couple of thoughts.

Obviously what you get is dependent on your buying power, perhaps start with the game cube specs and work on a budget around that initially. See how well it fits in with your research into components and their prices. Obviously set your budget and then add 10%-20% to cover unforseen costs :o)

Have a good look at what other people are building and see how the builds might fit your needs, youtube, hardware unboxed for example, the reviews in PC part Picker and various websites and forums, it will help you set a budget. You will also need to gen up a bit on hardware component functions and prices. Have a look at the component sellers websites and compare prices across a wide range of suppliers. It is worth doing the research. Definitely consider buying 2nd hand.

The type of games you play will affect the capability of your PC, so if you play the latest AAA games, you will need a better spec, but if you play older games or Indie games not so much.

AM4 and AM5 seem viable with current AMD support for both platforms, so you have a wide choice of CPU I think. I think AM4 and is more than adequate, in most scenarios but AM5 is newer. You could go intel with Linux if you're buying new, again needs the research, it might be more budget friendly and fit between AM4 and AM5 performance wise. If the drivers are not in the kernel, they should be easily obtainable.

Motherboard wise, look for something with solid VRM and the facilities that you'll need. Check to see that the MB you get does not throttle the CPU when it gets hotter under load. If its not a problem for you then you can buy cheaper.

Storage and RAM have gone up in price. You don't need to go for anymore space or memory performance than you need. e.g. the sweet spot for AM4 memory used to be about 3600Mhz. That figure is higher for AM5 memory, about 6000Mhz I think, but you can use 5600Mhz or 4800Mhz happily without noticing it. Sometimes the difference in performance is marginal and not cost effective.

You would need 16Gb RAM, maybe 8GB initially, depending on what you run, and then see how it goes.

Linux has a small footprint, so you may get away with gigabytes of drive rather than terrabytes, store your game files on an external drive perhaps.

You could get an RX9700XT or a plain RX9070 both with more than 10GB Vram, and both capable of 1440p. The 9070 because its performance is slightly less than the 9070XT but still capable of some raytracing. Intel GPUs have the VRAM you want so they might be worth a look, just make sure that Intel drivers support the games you play. Other 2nd hand GPUs are available.

I don't know about a TV with 4K at 1440p but I imagine that the bigger it is the better the text. When I changed my monitor from 1080p to 1440p the text got smaller on the same size screen.

HTH

edit, confusing VRAM with VRM