I wouldn't bother with DOS 3.x unless you want to be a masochist. You could do DOS 5.0 if you want somewhat leaner than 6.22 on disk space. You can still do himem+emm386+dos=high,umb with DOS 5.0 if conventional memory is what you're getting at. DOS 3.x can't do this without add-on utilities, but I don't recall what the conventional memory footprint of DOS 3.31 is.

Is there ANY advantage to Dos 3.31 , over 5.0a ??
I was planing to use this machine to also try out early '80s games, and was thinking that an older DOS might be more compatible..
But was also intending it for late '80s -to- early '90s (like 1992 max.) 3D games.

On a 386 I don't think so. Only thing I could see is if you don't want to use Emm386, then perhaps you'd have more free memory with 3.31 than 5. But I haven't even checked that.
Plus, with 3.31, you're going to have to acquaint yourself with the famous Edlin...

I found this somewhere: "4.x version would leave about 10K less conventional memory after loading, than does 3.3. But DOS 5.0 leaves about 35K more".
So MS-DOS 5.0a seems like a good contender! Especially since i can use with it my 1.2GB HDD 😁 😁

But is there a risk of some mid-early '80s games, not starting because of 5.0's memory management or something?

With cache disabled, and memory wait-timers added, the AMD 386 DX-33 that I have, seems to go as low as an approximate 16-18 Mhz CPU.. Coupled with the shittiest video card i can get my hands on, I'm having pretty high hopes for as low as mid '80s games 😀

If you have trouble with particular games you could always make a 3.31 boot disk just for those.

a boot disk.. as in.. a 1.44mb diskette ??

A floppy disk prepared as a system/boot disk. The usual command under DOS would be:

format a: /s

This will transfer system files to a floppy A: drive.

PS:
Error on the previous page: CHS = Cylinder-Head-Sector

Ou, thanks!
I completely forgot there even was such a thing for DOS.. (as in, DOS could make it's own)
Tho, I was a big fan of the Win ME system disk, back in the day!.. still am actually 😀