As anthk wrote, NetBSD would be a perfect fit. Don't know about Hyperbola, though it looks OK.
Anyways, I'd recommend something else, namely AntiX if it has to be Linux:
https://en.wikipedia.org/wiki/AntiX , either one of the options/images as listed from their mainpage https://www.antixlinux.com/ or rather this to go fully bonkers:
https://www.antixforum.com/forums/topic/antix-23-2-init-dive...
The thing with AntiX is, one can 'remaster' it on another system, to have a very customized installation image, stripped of anything unwanted, and added wanted apps, ready to roll on that poor Pentium thingy :-)
Easily, while running in 'live-mode', without having to recompile shit. Furthermore it has all sorts of installation options, which makes it really flexible without diverging too much from Debian, which it is based on. All with a few presses of function keys on keyboard, and some clicking around in their GUI-tools. Those are what makes it special and really useful IMO.
https://antixlinux.com/the-most-extensive-live-usb-on-the-pl... &
https://antixlinuxfan.miraheze.org/wiki/Remaster have some overview about that.
Now about booting that on a board which probably has only USB 1.0 or 1.1 at best, and its BIOS doesn't know shit about booting from USB, or added (passive, without their own BIOS-extension) PCI-Sata/USB/Combo cards in general:
There is an Austrian guy who solved that with https://www.plop.at/en/bootmanager/full.html , this worked for me somewhere around 2010 with cheap PCI-Cards for about 20€.
Just by pure Assembly-language in the MBR, and gave nice graphics, too!
Since there are DOM(Disk on Module/Flash to IDE in use, this seems unnecessecary now, but maybe not?
Other options would be https://www.plop.at/en/plopkexec/intro.html from the same guy, or
https://www.solemnwarning.net/kexec-loader/ & https://github.com/solemnwarning/kexec-loader
So that leaves the question of how to expand the capabilities of that mainboard.
USB3 would be nice to have, but I'd doubt that a P100 can push&power that in a really meaningful way. Furthermore they are rather expensive, though they exist:
https://geizhals.eu/?cat=ioexpcard&v=l&hloc=at&hloc=de&hloc=...
Personally, I'd waste two PCI-slots, one for SATA, to have the 'real thing', and one for real USB2 for peripheral convenience.
I'd go for the cheapest thing with the most ports and common chipsets. In case of SATA maybe even RAID-controllers because they tend to have their own BIOS which 'plugs-in' into the mainboard BIOS, and one doesn't have to use that RAID, under Linux they can just work as multiple, individual SATA-ports, and they would be bootable without all that DOM/Flash to IDE, and/or bootmanager crap! :-) Like these:
https://www.aliexpress.com/item/1005003285309722.html (RAID, BIOS!)
https://www.aliexpress.com/item/1005008117632551.html (RAID, BIOS!)
https://www.aliexpress.com/item/1005008763581735.html (they even mention Linux!)
https://www.aliexpress.com/item/1005007928947473.html (just 3xSATA(2 internal,1 external +1 additional internal IDE), probably no BIOS)
Or something like from here:
https://geizhals.eu/?cat=iosasraid&xf=614_PCI
For peripheral USB2 convenience, anything like these, which give four external, and one internal port:
https://www.aliexpress.com/item/1005006223700099.html
https://www.aliexpress.com/item/1005007371252877.html
Or something from there:
https://geizhals.eu/?cat=ioexpcard&v=l&hloc=at&hloc=de&hloc=...
anthk•4h ago
On the VM, FVWM (I can post mine if anyone wants it) will be the best option -you can disable opaque window resizing and moving- among a ton of CLI and light X11 tools such as "links -g", sxiv, xpaint and friends.
TinyCore will eat your ram once it you start installing stuff. It's better to get a true system installed.
On the CPU, a CLI system with tools like a Unicode XTerm, TMUX, Catgirl for IRC, Mutt... will fly. But if you can get some Pentium II or even better, III... your OS will fly and you will even be able to listen to some OGG/MP3/FLAC music outside of audio CD's.