I personally like the Asrock Pro onboard 10gbe FTW, and its not stupid pricing like the zenith and keeps your slots open
I wouldnt worry about a mono block unless your doing some crazy OC unless you have the worst air flow ever.
https://level1techs.com/article/patch-npt-ryzen-better-performance (not sure if you care about pass through performance or not )
Not sure about iommu groups last video i saw was https://www.youtube.com/watch?v=cDbn98QTAbg