For the cage and canvas, I'd lean toward keeping them for security, especially since you’re stopping at motels. Peace of mind is worth a few extra kilos. As for trailer brakes, you might want to check out
https://www.pedders.com.au/ in Hornsby. They offer a range of services, including brake installations, and could assist with your trailer needs. I found them when I was in Argentina, my guide from
https://gowithguide.com/argentina recommend me that one. Good luck with the build, sounds like a fun setup!