Better late than never:
286 (12 MHZ) - PC/MS/DR DOS 5.0/6.x with Win 3.1 or PC Geos(Geoworks/New Deal Office)
386 - MS/PC DOS 5/6/7/2000 DRDos-Novell Dos 6/7/ plus Win 3.1/WfW 3.11 or PC Geos (Geoworks/New Deal Office/Breadbox Ensemble)
486 (33 MHZ) - As above plus OS/2 2.0/OS/2 Warp3 Connect and Linux. With Dos maybe DesqviewX just for fun. Use any Dos 6 up.
Pentium 1 (75 or 100 MHZ) - As above plus Win9x. Dump maybe OS/2 v2 and use Breadbox Ensemble for a PC Geos enviroment, as lower wont run or had issues iirc.
Pentium 1 (166 MHZ) -As above Windows 95C/NT 3.x/NT 4.x
Pentium 2 (233 MHZ) - All the above plus W2k or Win98SE or OS/2 Warp 4
Pentium 2 (350 or 400 MHZ) -As above
Pentium 3 (450 MHZ) - As above
Anything else Linux/W2k/XP eComStation may be an option worth considering also.
You can combine some earlier Dos variants, namely MS Dos 6, with tools from Win9x to see more memory on later machines if needed. There's always FreeDos to have play with as well. BeOS and QNX ran marvelously on my Celery 400. If you got the right combination of hardware you have great choice and can use a boot loader to load your flavor of the day.
It'll certainly cut down on the number of machines required.