In my view, very little is needed to support the trains themselves. Honestly, they don't weigh that much. The framing is there because the lower level of the layout needs to support, first its own weight, and that of the upper level, and then the forces of being bumped, leaned against, and perhaps even knelt on to reach something way in the back. So -- if you are sure that you will not be putting your own weight on the upper-level section of your layout, then it needs no framing, just a few posts to hold up the plywood subroadbed.
How few? I confess that our layout was just slapped together, mostly out of scrap wood, but our benchwork has given no trouble, and parts of it have been in place for close to 20 years now. Our subroadbed is 1/2" OSB. On straight runs, there are places where the posts are 24" apart. You may not wish to live quite so dangerously, but that gives you an idea of what some people get away with.
BTW, "cookie cutter," as I understand it, means that the surface of the lowest level of the layout is a flat sheet of plywood. Wherever there will be elevated track, you lay down the track, trace around it (leaving as much extra width as you want) and then cut along the line with a jigsaw. This gives you an upper level that was cut out of the lower level. Elevate the upper level with some posts that are a little wider than the cutout (to span the gap you made in the lower level). Or else, run the posts down through the cutout you created, and fasten them to crossmembers in the layout framing.
