OS 3.9

[Minuous]

For OS3.5, you need Kickstart 3.1 (or better), 68020+, and 2Mb of RAM. Probably OS3.9 is the same, you might need perhaps slightly more RAM though, 3Mb or so should be enough I'd imagine.

You don't really need a CD-ROM or hard disk, but it's not much fun running it from floppy.

[Minuous]

Well, not easily, but there's no reason why you couldn't really. Not on a single floppy but on several if you fooled around with the startup-sequence it should be possible.

You could even run it from RAD:, I would imagine.