I’m impressed at the tinkering! Though, they literally have a guide on the official repo about connecting via serial, so maybe your UART efforts were unnecessary lol. I can tell you that if the board isn’t in a laptop, it will default to displayport over usbc just fine, so the edp to dp might not be necessary either - but that one could be useful later on if you wanted all four usbc ports for other things. But, I have a Dell USBC dock that I plug it in to, and it seems to work just fine - including USB. I used the top left port, maybe that matters? Serial is only through bottom right, for example.
As for the QSPI,
These links may offer a good starting point. It will likely require custom kernel parameters, so if you have an SOIC clip, it MAY be easier to just use that - though, accessing the chip requires removing the heatsink. This is very much a user preference thing at the end of the day. Personally, I feel like it’s “safer” flashing those chips with the computer off using an SOIC, but maybe that’s just unnecessary paranoia.
If someone got coreboot (or oreboot) working on this board, I think I’d cry happy tears haha. I don’t understand people who think uboot is better. From the manufacturer POV, sure, I can see it. But, it’s literally why so much of this is a hassle. It’s 2025, imagine using dip switches to choose a boot device 
Much harder to read with a clip, and near impossible to desolder because of the huge pad underneath. Unfortunately I think reading it out through Linux is probably the easiest thing to do.