Length is fully up to you, I would recommend placing one Mount every 50cm depending on the magnetic strength of the magnets, theoretically it’s possible to also screw them in place but thats not always an option with the way the mounts are designed.
Magnets i used: https://amzn.eu/d/ihZeDba
Designed to fit with a 11mm SW Stainless Steel hex bar (https://www.ebay.de/itm/196785133359?mkcid=16&mkevt=1&mkrid=707-127634-2357-0&ssspo=MITvQYTzRiS&sssrc=4429486&ssuid=My2EcWHeSWS&var=&widget_ver=artemis&media=COPY )
The small holes are for M3 screws to lock the bar and make it a bit more stable against the wall
The author marked this model as their own original creation.