I'll eventually get into using boost and all that other Jazz I'd like to just get a comfortable knowledge of it's behavior without any of the added features CPUs do nowadays like Boost, the PBO thing, etc. I kinda want to see how cool it'll remain at a static 3.9GHz with the NH-D15.
I've seen reviewers do 4.2 GHz static with a 3900x on an NH-d15 (albeit with temps in the 80s), so 3.9 should be achieveable on a 3800x. My 3900x will do 3.9 GHz at probably 1.15v depending on the workload. 1.2v easily. It seems that 3800xs are binned a little better so you should see the same or better behavior out of a 3800x.
Boost behavior is much improved with AGESA 1.0.0.3ABBA, so depending on your workload, you may prefer default behavior to static. I think my gaming performance is now better using default (and some funny tricks with LLC and offsets), but my full MT performance is somewhat better with static clocks. I think an NH-d15 should at least get you to 4.2-4.3 GHz static which is where MT performance starts to pull away from updated boost behavior.
What's the cliff notes on things for Ryzen on Windows 10? Is Ryzen Master necessary? Is that Ryzen power plan necessary? What else is there?
Ryzen Master is not necessary, but it's very useful. Just be warned that if you use it to tweak any memory settings that it will lock out some settings in your UEFI. You will be unable to change them with anything but Ryzen Master until you uninstall Ryzen Master and reflash your UEFI. Ryzen power plans come with the chipset drivers (which you will want), and for my uses, the Ryzen Performance plan is the best. Most people have been messing with Ryzen Balanced, but if all you want is raw performance . . .
Anyway, just make sure you install the latest chipset drivers, and make sure you have 1.0.0.3ABBA as your AGESA version (check the UEFI, it should tell you). Set Ryzen Performance power plan and you'll be good to go. I can make recommendations on LLC settings later, though that may be board-specific.