Does the upper part the models would stand on detach separately?
Sort of, the underside of the walk way is actually flat, so sadly the cables can not be seen from under the walk way itself. The trade off is that the walk way has hex holes, so you can attach pillars, ladders and connect different length walkways together without needing a load of pillars. That said, I'm a bit gun shy as to how much weight those joiners can hold if they were not glued in and there is also a piece that you can glue in place on top to reinforce the join.
The barricades on the side are detachable, but they will damage the paint if you take them off and on. You could work something up with magnets if you really wanted to.
I saw Tabletop titans do a board full of the walk ways and shipping containers (CWE vs Tau) ages back, on their youtube channel. I really liked the concept, kind of like an over sized zone of mortalis lol. Love the idea of having movement on multiple levels rather than just hiding in buildings. The 40k conquest mag issues 79 and 80 made it cheaper to kick off the project.
On a side note, check out their video on how they setup their game boards (you'll see one of their walk way maps in there) https://youtu.be/lTVSTduzf-M