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.
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.