any position at the ends. Height above base is only thing, 50mm or thickness of standard styrofoam insulation. Maybe you will be lucky and find some discarded in a skip.
Need some means of wiring between boxes. I use Hifi stereo sprung speaker connectors, others use chocolate block connectors, just remember which wire goes to which rail.
Links between boxes are short lengths of track.
Almost forgot, boxes are on their sides, giving more height but less track space.
Narrow gauge Francophile interested in 1m, 60cm,50cm , 40cm and smaller gauges . Build in scales from 1/6th to 1/24th. Also 1/32nd and 1/35th using 16.5mm track to represent 50cm and 60cm gauges. http://www.rue-d-etropal.com