I run one of these on my router (OpenWrt 22.03.4, r20123-38ccc47687) so it's tested and working. I'm selling these at the same price I got them for, so $42 each. You just have to pay shipping to where ever you're at, shipping from California. Getting these direct from AsiaRF costs $30 in shipping so about $70 each. Comes with a heatsink. They also support DBDC so they act like a 2.4ghz and 5.8ghz AP at the same time (they have 2 wifi radios onboard).
With my laptop with an Intel AX210 wifi card, I'm able to get 1.2gbps.
Sorry for the slow response. I think I have 3 left.
That's how I use mine, in a x86 board with a PCI-e to mini PCI-e adapter. I believe an atx mobo's PCI-e spec is 3A so pretty close. Either way I've never had an issue and get 1.2Gb/s line of sight.
Also if you're very concerned about the 3.5A you might be able to find a nice pcie adapter that has an onboard buck converter to provide the extra amperage. But I'd only try that if I found I was having issues with power.
I don't know of anything that can do that. From my understanding you'd need a chip that would act as an interface from pcie to usb. The closest thing is those nvme to usb adapters. But those chips appear as storage devices that then do the interfacing to an nvme drive themselves.