Thanks for the info. I will double check on those screws. I initially used the plastic ones you described, but realized later I needed them for the light mount.
The hanging kit should have came with a set of metal set screws to secure the location of the mounting plate. I did swap my metal ones out with easier to use plastic thumb screws I had laying around that came with the modules. You can extend the center rail without any issues as long as the surface you are mounting it to is secure.