The asrock b450 is a fine motherboard, it should work with the ryzen3000 series, but ryzen 4000 is a bit different question.

Usually stores update the bios for free, you could do that if you somehow get an older motherboard without a newer bios.

The difference between ryzen 2000 and 3000 is too great, i wouldn't get a 2600.

One really important thing!

I don't see a graphics card anywhere on your list? Do you already have one?

Because the normal amd processors don't have any igpu, so you can't use them without a video card. Only the ones with the 'g' suffic have onboard graphics, for example r5 3500G.

I have the GTX 970, it's just a upgrade package to get new CPU, RAM, MOBO and WiFi since PCI not express is not a thing anymore...

Then the build looks fine!

Ok so then I will check for 3000 sticker, if not I will ask store if they can update BIOS if not it's better to spend 1k or more for B550 board.

Mhm. B550 is only good if you would want to use ryzen4000 too, but for the 3600 it will work fine.

The B550 board has built in wifi 6, the other store has ECC RAM at 2666MHz so once they get 3600 back in stock that offer looks better but 1k or 1.5k better is what I wonder.  

Yeah, but does the motherboard you want to use support ECC ram? Not all ryzen motherboards support it, and afaik they were in the minority, especially in the early days, dont know if that has changed so much?

The RAM was listed on the ASUS TUF series, ASUS is a very pro company. Also it had PCI 4.0not sure that will matter much?