You just throw it on a USB and flash the motherboard. You don't need to build a PC, update it, then tear it down and do it all over again. Also... $150 CPU and $500 GPU? That's...not bad. It seems like you don't know what you're talking about, considering you didn't know how to flash a MOBO, so I'd be wary of offering advice and criticizing someone next time.
Ryzen 5 2600 + RX 5700 ($150, $500) is a very common and very good pairing. I'd recommend dropping $50 more and getting an R5 3600 just so you'd have the option of upgrading the GPU at a later date but...that's still $200, and that's future proofing it.
https://pc-builds.com/calculator/Ryzen_5_2600/Radeon_RX_5700/0Qj14f28/ (2600 w/ RX 5700)
Incorrect, the GPU has the most significant impact. An R5 2600 is $160, an RX 5700 is $500. The golden rule used to be a CPU should be 1/4 the cost of your GPU.
You can buy a windows 10 key off ebay for $3.
[s]I haven't seen it in this thread, but you could save $150-200 by going with a microATX board.
1. Make sure it has a good VRM heatsink for reliable OC
2. These can hold 32GB of RAM, I don't see that being outdated anytime soon; but if you want to drop over $200 for 64GB of ram, you do you.
3. Since everyones recommending mid-tower cases, a microATX would make sense.
I assume you're only going to rock a wireless card and a GPU at most, so the extra PCI-e slots from a regular ATX are redundant. Don't pay for extras you don't plan on using.[/s]
Don't spend $300 on a MOBO as said before, but disregard microATX stuff and get: https://www.newegg.com/msi-b450-tomahawk-max/p/N82E16813144267?Item=N82E16813144267
212evo/deepcool air coolers are perfectly fine and you'll save $100 from not getting an AIO. I rocked a $100 microATX, 212evo and a 1660 equivalent for many years. I switched over to AMD and I'm using a $30 deepcool and it's serving me very well. My only gripe is that my 212evo was old enough that I didn't have an AM4 bracket so I had to get a new after market cooler.
Only problem is the 1660 is getting dated, drop the AIO and save $100. With that $100 you can go from the 1660 to an RX 5700, and get a ~20% improvement. For $100, that's good; as a 20% improvement over the RX 5700 would be a 2070S - a $300 upgrade.
Be careful buying parts right now, some people have recommending $300 MOBOs that are normally $100. A lot of people spent their coronavirus stimulus money on PC upgrades and stocks are low, prices are skewed and being upsold.