Building a PC

You know how this works
A budget is a good starting point
Example games?
Which monitor are you using?
Etc.

You need to set a budget first with or without a contingency. Then decide what minimum specs you need for processing power, memory and storage. If you get a cpu with integrated gfx you can run that initially and then add a decent gfx card later if needed.

As for size, you can get micro / mini pc's like Intel nuc or mini itx. But to be honest your going to pay more for one of those than a bigger system. Plus your limited by the size and space available to add extra memory, storage or graphics cards.

Stick to standard micro atx / atx and a decent sized desktop, mini or midi tower case.

From your laptop specs. Looks like your going to want ryzen 5 / 7 (9 might be overkill) or Intel i5 or i7 12 or 13th gen. 16gb or more ram and 1 or 2tb ssd, as any bigger and your going to pay a lot. You can always add more drives or even a large internal or external hard disk cheaper.

Bear in mind there are still chip shortages and some things are still in short supply. Also the new platforms and chipsets are out along with ddr5 memory which is expensive and soon to be available PCIe 5.0 ssd's. Speeds and latency on ddr5 is not great at the moment but will improve quite quickly.

If you're doing this as a cool project then the first thing to do is identify which bits you're interested in. Where do you want to splash out and get us to help you find the most interesting version of something, and where do you want something reasonable to fill in the gaps?

Personally I tend to find the case and cooling bits interesting, and the computing bits inside fairly dull but others get something out of owning the expensive versions of a chip.

It's safe to say any new desktop will equal or better your laptop. Whether it's an upgrade would depend on how small an improvement you'd consider an upgrade, but that's a pretty recent laptop so getting something several times as fast might be tricky/expensive.

There isn't any agreed upon sizing terms for cases, so you're better off giving rough dimensions rather than terms like mid. Shape preferences are also handy - is a tall slim case preferable to a short, fat one? Does depth matter?

Or you could always buy a prebuilt PC.