That SuperStrut appears to be galvanized already, so it should hold up well to the elements - I'd probably just rattle can it and save the expense of the powder coating. I don't know what kind of deal you'd be able to get from your friend, but I'd assume you'd spend more for powder coating than...
Static load of the roof, yes. Not necessarily the static load of the rack itself. Is that not the case? Also, all the aftermarket racks are likely be more rigid that the OEM main rail, and therefore be capable of carrying more weight, wouldn't they?
Likely correct. I was thinking...
I'd think an aftermarket rack is going to be more sturdy and support more weight. Due to the more rigid materials used and additional mounting points.
And this times eleventy billion.