Pre-production windowed side panel is super, super nice. This case is everything I hoped it would be.
The bottom fan test results were interesting. I tried EK Vardar EVO 140ERs, Noctua P14s, and Noctua F12s. It turned out that putting the Phanteks Halos underneath the fans were the best configuration for low GPU temps. That configuration also took care of raising the fans off of the bottom grille. (Fan intakes pressed right against a grille produce a ton of noisy turbulence, especially Noctuas for some reason.)
Of the three fans, the smaller F12s won by a wide margin, almost certainly because of the static vanes on their exhaust sides. Both 140mm fans had a sweet spot around 950 RPM beyond which turning them up any faster yielded higher GPU temps. With the F12s, faster was better, all the way up.
120mm fans don't completely cover the bottom grille area. Adding a blank plate under the bottom fans to cover the extra grille area surrounding the fans made a huge difference (5 degrees C) across the RPM range. Hot air recirculation is no joke!
In the end, I didn't bother with dust screens at all. All of the intake fans spin down to zero at idle, and my house isn't that dusty, so I'm just going to run it like this and see what happens.