If you're not doing multimedia processing, then you only need 16GB. For gaming purposes 32GB is negligible. As far as motherboards, the ones with the best VRM is necessary if you're into extreme overclocking, if not then don't bother and find the most price efficient and any features desired. Personally I look for boards where two M.2 SSD slots can be used (preferably with heatsinks that go on top of them) at the same time that do not deactivate or slow PCI x16 lanes. G.Skill is the best brand in my opinion for RAM and has been for AMD processors in particular, CAS16 is cost effective, CAS14 if you want to splash the cash on RAM.
During that last Zen release, Asus, ASRock Tachi, and Gigabyte were among the best as far as releasing decent higher end boards. I would assume it would be the same this time around, but its best to wait for reviews/comparisons and checking every feature/compatibility before buying something.