That motherboard has one 4-pin CPU fan header for your CPU fan to plug into and two 4-pin fan/pump headers for your case fans. Since you’ll have two fans on top, blowing out, and two fans on the bottom, blowing up into the case, you’ll want the top fans connected to one case fan header and the bottom ones to the other. You’ll want to use a Y splitter for both sets, so you can connect two fans to a single header. Something like this.
Planning on getting this fan header. (Ignore that it’s a 2 pack.) My motherboard only has 3 fan headers including the CPU fan one, so would this plug into the “sys fan” port on my mobo, or somewhere else?
You're looking for a Y fan splitter. Example for 2 fans: https://www.amazon.com/Rosewill-Splitter-Duplicator-Converter-Adapter/dp/B076HBQTD5. Example for 4 fans: https://www.amazon.com/DZS-Elec-Splitter-Sleeved-Extension/dp/B07FNQC63R?th=1
Fan header splitters....you're welcome here
You have a cooling system. The Ryzen 5 3600 comes with one from the box. It will be adequate for everyday use unless you start overclocking or trying to squeeze every last bit of power out of it. Then you can get yourself something simple like a Noctua U12. If you get the MSI B550i and want an aftermarket cooler, make sure you get one that uses the stock AM4 backplate. The MSI B550i uses a custom backplate and using an aftermarket one could crush the back of the motherboard. The Noctua U12 uses their Secufirm2 mounting hardware, which conveniently uses the stock AM4 backplate. Perfectly safe for the MSI B550i motherboard.
The H210 case also comes with two fans. I suggest you get a set of these so you can put both fans into one header. If you orient them as exhaust on the back of the case and the roof of the case. It'll suck air out in a negative pressure configuration. And by some insane/genius design, it works really well when paired with the short SFX power supply that I listed for you. There is however one thing you may need that is not on this list. I recommend a set of extensions. Not for aesthetics, but because SFX power cables are really short and may not reach far enough in this chonker of a case.
Have fun with your build! Feel free to ask any questions as you get them.
Will these work?