Gaming PC on a budget

[JEMC]

I'd wait to see what others with more experience than I have to say, but what I'd do is, after checking that everything works, try to find the latest BIOS for the motherboard and install it without changing the processor. Once that is done, change to processor and boot it up to make sure that it works.

Reinstalling Windows may be the best course of action, but I don't think it's required.

If the new GPU is from a different brand than the old one, like from an Nvidia card to that Vega 56, I'd suggest running DDU (link) to unninstall all Nvidia drivers and do a clean install with the AMD ones, to avoid problems.

The CPU cooler may work fine once you've applied new thermal paste, but there are software that tells you the tempereture of the CPU. If it runs too hot, you may be forced to get a better one.