How does this build look https://pcpartpicker.com/list/p2xN6R ?

I'm curious if the mobo will work with the ryzen 3700x out of the box and I believe that mobo should be fine in a mid-tower case? Just looking for suggestions or advice before I bite the bullet and buy some of these parts.

Mobo will work with the case in that build.

As for working with the 3700x... there's really no way to tell until you get the parts. IF the mobo has the latest or late enough BIOS then yes. If not, AMD has a deal where they will loan you a CPU for the purpose of updating the BIOS.

https://www.amd.com/en/support/kb/faq/pa-100

Why micro atx?
Newegg and Amazon are selling refurb B450F Strix for around 100 USD

Also get a better power supply. I feel like that 550CXM is gonna feel pain