What's best to do?? classically speaking

I have a Compaq Portable 386... Classically speaking... what is best to do in the cases below? 1)I am running dos 6.12, but I am thinking about re-installing with DOS 4 or DOS 5. Or more generally is it better to use a circa operating system or a modern operating system (Assuming the machine will run both) ? 2) The machine came with a 5 1/4" diskette drive, I am considering replacing that with a 3 and a whatever" drive, or once again more generally when one has an older machine is it good to upgrade the hardware to make it more usefull. I suppose on my single machine no one cares really, the "historical Police" will not appear at my doorstep. Let us extend the argument, Given a running PDP/11, what of the person who installs a current day 60GB disk drive and DVD CD ROM? Curious in San Jose. BTW I have two of these portables and recently offered one in trade for a part, I am also willing to sell for cheap. _______________________________________________________