One very simple question, in fact:

WHY. OH GOD, WHY.
http://imgur.com/a/rRAYQ

Is there anything to make it easier to keep track of what's what here? A simpler way to set up some rather simple, basic logic without sacrificing such a ridiculously huge footprint?

If [Iron] < 500 Go fetch [Iron]
If [Copper] < 500 Go fetch [Copper]
If [Both] < 500 Each Go fetch [Both]
If [EmergencyStop] Go to [Garage] and stay

That's all I'm trying to do here.
Where do I need to sacrifice the goat?

Haha, I was thinking of a mod that provides a Lua script interface to AAI might be practical, instead of combinator hell :-D

That would be very dope. Goats are difficult to get so far away from earth.

If you want a hauler to have multiple destinations, you need to set up a priority signal for which to act on if more than one are satisfied. I just use red signal with value 1, but you can use multiple colors for more destinations. Set a combinator to output everything when the color signal is > 0, include in the input the destination for the hauler, and connect that output to the controller.

See my post on the forums for this mod for an example.

If someone wants to write a scripted interface my mods already provide all of the required remote interfaces for that to work.