Models showing up purple

mat_specular 0 ; buildcubemaps ; map [name] ; mat_specular 1

I was told you need to reload all the materials, either by switching to a different map, then coming back, or doing the reloadallmaterials command.

I'm not 100% sure on that, but this was the list of commands I was given to build cubemaps when compiled in LDR

You don't need to reload the map or the materials. Once you do buildcubemaps the reflection textures are written into the BSP, and it's done. You just won't be able to see them right away unless you tell the game to reload all the materials one way or another, but unless you want to take screenshots or something you can just quit and the map will be fine for other people.

mat_specular actually turns the reflections on/off, that why when you did it with 0 it looked "fixed" since it was no longer trying to render a missing texture. As frozen said though, you want to turn them off before doing buildcubemaps otherwise the purpleness will be visible in the reflections (the command literally takes a cube of screenshots). Then obviously you want to turn them back on afterward.