1.: It's a Fujitsu 1080p LCD 🤣 (with HDMI). Issues only in GRUB, bios setup worked just fine. (Maybe too high res or something? I could try to get a DVI to HDMI adatper to check. Or a lower res Samsing TV-monitor)
2.: No floppy means probably no DOS. I can see if I still have some official WIN98 discs laying around. IDK why the stupid thing doesn't reliably works (swapped the drive AND the cable multiple times).
3.: Thanks for the tips, will look out for them
4.: If you wanna give some more tips on something I got a separate thread for this thing (actually a couple). Don't wanna drift away from the main topic here. (HDD not detected properly when FDD is, and vice versa (My Pentium III saga, part 3))

Quick edit: I live in Hungary, so anything further than Germany or Austria is probably a no go xd