Hi Andrew,
There are several Mother boards available depending on what size unit you would like to build - ASRock B450M Pro4 is a good board , mine is coupled with a Ryzen 3 3200G processor. It can have 4 SATA 3 disks but if you use the M2-2 you lose one of the SATA sockets.
If you are interested you can download the manual from ASRock site. The wired network socket works but I can't say anything about sound because I don't use it on the computers.
Thanks. It occurs to me that, realistically, there may not be that many m/boards we'd want to run AOS on. Lenovo and ASUS may be It, because building good hardware will be trickier at today's speeds. Back in the dawn days of (semiconductor) PCs, we goshed and wowed at the whizzy clocking of CPUs. Eg: Intel 8080, 800 kHz; Zilog / Mostek Z80, 1-4 MHz; Hitachi CMOS Z80, 6MHz... No idea about others, like 6502 and 6800 -- assume "slow as cold treacle" alongside multi-gigahertz jobs in which signals travel via what are more like transmission lines, where precise dimensions and materials matter. With folks needing reliable functionality, newbie manufacturers are best left to sell their stuff to users who can abide beginner design work. No?
I'll see what I can make of the various helpful pointers you-all have supplied.