Let's presume that the driver set that is available limits the hardware available. So far I'm hearing:
CPU: 32 bit (is there a 32 bit multicore that you'd prefer? Or would we have to have a 64 bit processor to have a decent multicore option? Arca does handle multiple cores, correct?)
AOS supports multiple cores fine, does not support hyper-threading, seems to work fine with the AMD equivalent though I personally haven't tested.
Basically the newer the CPU, the better for performance and multi-core due to shared cache and such and as all CPU's have been 64 bit for quite a while, we'll end up with a 64bit in 32bit mode.
64bit CPU's also do PAE well for that ram disk in memory above 4GB (actually 3.5GB or so)
UEFI compatability mode or Legacy BIOS support
Storage: SATA harddrives and optical drive (Limited to DVD? Does OS/2 use Blu-Ray, Blu-ray burners?)
Blu-ray works but we're behind on the latest UDF file system so it is like a big DVD.
Input/Output: PS/2 mouse and keyboard, serial, Parallel ports, USB 2.0
Sound: Soundblaster 16? (Does OS/2 do USB sound?)
Yes OS/2 does USB sound. As for the Soundblaster 16, I used a PAS16 (Pro Audio Spectrum) for a long time and I was quite happy with that. It included a Soundblaster clone so 2 sound cards in one and most DOS games worked with the PAS16 and those that didn't worked with the SB.
Others might have other favourites such as a Gravis card. Ideally would be an ISA slot to plug in one of these old cards
Video: If SNAP drivers are all we have, what's the best video chipset/card for this? VGA output? DVI?
Probably an ATI X850, which should support DVI, VGA and dual head (2 monitors).
I'm currently using a NVIDEA GeForce 7300 series, kind of slow and didn't work with DVI.
The Panorama drivers work pretty good with Intel or ATI chipsets, modern CPU's are fast enough to make up having to run in VESA mode and it patches the mode to support wide screen monitors.
For me, all of this would have to support the DOS and Win_OS/2 VDMs as well.
Need older sound cards for DOS and WINOS2 support. For full screen DOS, video probably depends on the programs video support, all the GRADD based drivers (all current) support WINOS2