Thank you for sharing, I'm gonna save this comment and come back to it. I'm in Vietnam and chose this case partly because it seems resellers do have it in stock here. It's all the other stuff - custom risers and cables - I'm worried about.
I'm gonna target a 4080/5080 - stuck with Nvidia because CUDA - which gives me a lot more wiggle room with the power supply.
I've built plenty of PCs, including a few SFF PCs without GPUs, but never something requiring this kind of customization so I'm planning to find a detailed build online and mostly copy what the other person did, if possible.
If you go for the 4080 or 5080, you will have a lot more options for sure. If you can find one, I would try get a 2/2.5 slot wide card, gives you so much more flexibility.
Bookmark this Excel, saves you a lot of time looking up specs: https://docs.google.com/spreadsheets/d/1AddRvGWJ_f4B6UC7_Ift...
You want a GPU no longer than 325mm (though exactly 325mm may be pushing it).
For the 4090 it was basically Founder's Edition or my card. FE was impossible to source (I am not in the USA), and I had to get the MSI card specially ordered in, the most common card was the ASUS ROG monster which at 357mm would never fit.
At 322mm, the MSI card barely fits (after deshrouding), there is like 2-3mm to spare length-wise. And you have to build in 3 slot mode if you want any clearance from the PSU (mount PSU on standoffs).
Before deshrouding, the GPU plastic covers mean you can't also plug in the USB-C I/O port.
Oh yeah, forgot about the riser cable.
The one that comes with the FormD case is serviceable, but depending on the motherboard. I believe it has issues with Gigabyte B760 and B650 motherboards.
I also have the LinkUp 19mm PCIe 5.0 V2 riser cable (https://linkup.one/linkup-ava5-pcie-5-0-riser-cable-future-p...), but it can only be used in air-cooled builds - it has a red tab at the top which blocks the radiator if you want to use it with watercooled/AIOs. See this thread: https://www.reddit.com/r/sffpc/comments/1f5ij02/question_re_.... Some brave souls have hacked off the tab with a knife/scissors but you have to be careful not to cut the wires along with it :)
So I had to go back to the stock cable for the AIO flavor build, which has other issues (you have to fold it/squash it a bit at the bottom where it bends around below the motherboard, so that pressure on it doesn't cause it to make it pop out of the motherboard connector). Before you put on the bottom cover with the feet on it, the riser will touch the surface of whatever you are building on, and given enough time can cause the motherboard connector to loosen or pop out.
Had hours of debugging fun trying to figure out why it was starting to lock up while gaming, turned out to be the riser having wiggled loose from the motherboard.