So here's the supports on the ceiling and wall. Nothing special, just deck-screws into joists, but I did have to move the support-points because of the skylights...
... and once that was up, it wasn't much of an issue to get the actual rack mounted up - it was actually surprisingly easy. I just connected the two carabiners closest to the wall, then the two closest to me. Since I'd already worked out the separation distance (51") it really was just a matter of positioning the eyelet hooks, tightening them, and clipping the rack to the support.
Wires are still a bit messy up top because I can't find the second set of magnetic hooks for the rest of the lights, no point tidying it up until I have all the lights on there.
Overall I couldn't be happier with it. The magnetic hooks attach with a reassuring thunk and the only way to move them is to angle them before pulling them off. They aren't going anywhere.
It also lets me place the lights exactly where I want, and if I change my mind, I just move a magnet and maybe do a bit more wire-tidying
