Ultra_DTA: I have pretty limited knowledge of PC hardware/components and software/compatibility troubleshooting.
Google is your friend, that's how I've learn most of the stuff I need to know (also related to PCs, and administering/using e.g. Linux), ever since Google was a thing. If you have a question in your mind, just write the question, maybe in a simplified format, to Google. It is quite probable you are not the first person in the world asking about it.
Ultra_DTA: I'm also pretty unfamiliar with the longevity of gaming PC builds (i.e. when upgrades are needed).
When you are not happy with how smoothly and fast your games are running, then it is a time to upgrade.
What is different from consoles is that you can also change all kinds of options for games' graphics and such, from within game options, in order to make them either look better (and run faster), or run faster (but look worse), to better suit your specific PC configuration and your own tastes (some games you might want to run smoother with less impressive graphics, while some others you want to run with best possible graphics, even if they ran somewhat slower then). On consoles you don't have to care for such options as everyone has the same machine configuration, and hence I guess console games don't even give you different graphics options much.
For instance, if I try to run a demanding new-ish AAA game on my 5 years old gaming laptop which I know is by now struggling with newest heavy games, first I usually switch graphics resolution to 1280x720 (instead of full HD 1920x1080), and maybe disable some eye candy from graphics that I know are demanding and not that important, to see how well it runs.
Ultra_DTA: With that said, my fear is dropping $1k+ on a build and having something go wrong with hardware or simply not getting the most out of it because of my lack of knowledge.
The graphics card/chip (GPU) is usually the component that you need to ponder a bit, rest of the stuff (including the CPU) is pretty generic. At this point I'd personally just go with some mid-level, popular NVidia Geforce GPU which is common among PC gamers.
As for the rest of the components (if I was looking at a desktop PC), I guess I'd try to make sure the power unit (PSU) has enough power, in case I feel I might be using lots of power-hungry peripherals with the PC. It is better to have a "too powerful" PSU than one which is operating near its limits.
Then again since I personally nowadays buy only (gaming) laptops, I have to care less about the components besides the GPU, as I can't choose nor change e.g. the PSU on a laptop. It is what it is.
EDIT: Oh and the amount of RAM... I guess 8GB is still barely enough even for new games at this point, but I'd personally go with 16GB RAM right away, just to be more future-proof. When I think of my old and ancient PCs that I want to use for some purpose, like install Linux on them etc., the first thing that usually occurs to me is "I wish it had more RAM". Like that very old Pentium desktop PC I have, I wish it had 2GB RAM instead of the current 1GB, I'm pretty sure it would run Linux and web surfing smoother then.
zlaywal: And buying a SSD goes a long way in term of performance.
To elaborate: only as far as load times go, not e.g. the game graphics or such. And on the flipside you can install and keep much less stuff on a SSD than on a HDD, or then pay an arm and a leg for a big SSD.
So yeah, when I was playing Team Fortress 2 with my friend side by side (I have a laptop with slower HDD, and he has a laptop with SSD), yeah he could enter the match a bit earlier than me because the level loaded faster for him, but that's all. Otherwise the game ran identically for us.
Admittedly, with online games like Team Fortress 2 it is not only the hard drive speed that decides how fast a level loads, I guess it has to download and send some server data for both of us as well...