Need advice on building an elevated loop on my layout.

I am considering adding an elevated loop of track to my little 5’x9’ layout. It occurred to me that I really don’t know the best way to do this. I have both Lionel O-27 track and Fastrack, but not a clue which one would be best for this. Should it be supported on a plywood roadbed, or would the track be stable without it? How far apart should the supports be spaced? What else haven’t I even considered yet? Any advice will be greatly appreciated. Thanks.