Been a while since I visited this forum... but in the order from most critical to least critical:
1) Drone Hubs need electronics for their maintenance, not machine parts
2) You can control how much of a commodity goes into storage. There's a slider on the dialog window... upper right IIRC.
3) I personally use Universal Depots to keep one Sol's worth of the materials required for maintenance and manufacture near the Drone Hub that is most likely to do service a building. They're nice for this, because they house multiple types of materials, and you have finer control than the more specialized depots. I use said specialized depots for overflow storage, or to place large amounts of material on site in advance of a large project.
4) You will never get perfect control of what goes where, especially when your short on materials. The Drones will do their best to fulfill requested quantities first, and once that's done, they'll place materials in the nearest depot that accepts them, regardless of how full or empty the others are. When there's insufficient materials to fulfill all requests, the drones
seem to prioritize the universal depots first, but don't quote me on that.
5)
Shuttles, on the other hand,
seem to want to even out material storage between all depots on the map, once all requests are fulfilled. In the current game I'm playing, I watched a flock of shuttles deposit concrete from the
main depot in my colony onto the new concrete depot I'd placed for a remote concrete gathering outpost. Again, don't quote me on that.
