You'd want to wait for fall at least, for the new GFXs to come out, specifically the 30xx Nvidia ones which supposedly are going to be much better than the 20xx and not too expensive(but that remains to be confirmed). Not sure if AMD is coming out with new stuff soon too for the CPU, but generally speaking for gaming if you have high resolution(especially 4k but even 1440p) you'll be GPU capped rather than CPU capped and most current CPUs will do the trick just fine.
As for a guide to build, I'm sure more or less any done in the past 2years should be about what you'd need. Building a PC is surprisingly easy nowadays, and there's instructions on how to do it in both the motherboard and the case manuals(depending on what case you're buying but mine had instructions).
It's mostly time consuming to make sure you're not fucking anything up and getting all the fucking cables to go where you want them to go and shit like that, but the actual assembly is only a few minutes and most pieces have markers and blocking plastic bits so you can't actually plug them in the wrong way.
The only noteworthy advice I'd say is to get a small screwdriver(phillips type I believe is the english term, the x ones) if you go for a NVMe SSD(and you probably want to) since the screws on these fuckers are really small(M2 screws in fact, which is also in the name). Other than that a standard screwdriver and a bunch of time is all you're really need, people also recommend anti static wrist straps and while I built several PCs back in the days without one without an issue, I bought one with the last one just in case of.
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