@Anklebiter 192GB RAM works, but I only recommend the 4x48GB Corsair Vengeance Kit. Don't try to save money by getting two separate 2x48GB kits, as you're likely to get memory errors and system instability (this happened with me when I tried to combine two 64GB kits previously).
Also, TB works mostly fine for me on the z790 ProArt. Even sleep/wake works! I'm using an Apple Studio Display and an OWC TB3 NVMe enclosure. On occasion, if my computer crashes, I need to power-cycle it a few times, and warm-boot/restart a few times before the Studio Display gets picked up again, which is a little annoying. Another work-around is to boot into windows, and unplug/re-plug the monitor, and the TB controller will "wake up" again, then it'll get picked up by macOS
I imagine that using an eGPU through TB 3 won't be much of an issue, but I suspect that it'll be a bit frustrating if you run into the same scenario I described above. (never mind, I just read the note about the TB Bus not getting activated, which means no eGPU) My recommendation is to run two GPU's internally (a 1200W PSU should be plenty, as the GPU's rarely ever spin at 100%, even when I'm rendering with Redshift, Octane, etc). I'm actually running 3 6900XT's internally (the third one is plugged into the bottom PCIe slot with a
PCIe 4.0 4x to 16x extension due to a lack of space, with a 1600W PSU, and I haven't had any issues. Just make sure you have plenty of ventilation (the Fractal North case is great for that).
At one point I was running 4 GPU's internally on the same 1600W PSU. the 4th one was plugged into one of the NVMe slots with an
NVMe to PCIe 16x extension but it got a little annoying with all the cable management, so I just settled on 3 GPUs. I actually ran 3 with just a 1200W PSU for almost 3 years on my previous system, so you should be fine, power-wise.
In theory you could even run more GPU's if you want to fill out the other NVMe slots
and TB3 ports, but at a certain point you'll get bottlenecked by the Chipset's PCIe lane allocation (forget how many lanes the chipset offers on this board), and your PSU (although you could always use multiple PSU's if you want).