Motherboard standoff screws are machine screws, so how do I fasten those to wood securely? Can I forgo standoffs entirely since wood isn't conductive?
Also, I'm looking at a spare Radeon RX 5600 right now and I can't find any holes that would make suitable mounting points (RX 7900 XTX is what I actually plan to mount).
I see an L-bracket under the PSU so at least that one looks straightforward at least.
Edit: It looks like that PCIe ribbon comes with a mounting bracket attached. Maybe that's how they did it here.
I think I read somewhere that this isn’t good for thermals. It would only ever stay at ambient temperature, so it wouldn’t benefit from cool air being moved through the case and past the components
It's fine. The usual cpu, psu and gpu fans locally cool the hot bits, just as they would inside a case. You don't need case fans if there's no case, because the volume of free air means convection moves it away better than any case.