No they cannot, your customs office is like a station hangar that can only hold 25k m3, other people can't access it. They can however access stuff you launch from your command centre as it spawns like a can in space, but iirc it only takes 500 m3 so its shit
Plasma planets can be set up for a robotics chain on one planet alone, but bear in mind some resources are more abundant than others (and of course more valuable than others). Meaning you have to waste your grid/cpu on mining terrible worthless crap to sustain your chain. Оn thе plus side it packages down nicely. The hardest part about this is the fact your resource hotspots could be on the other side of the planet from each other‚ so your links will chew through your powergrid like no tomorrow.
Heres how it works:
Step 1: Basic Industry Facility turns 3000 units of raw materials into 20 processed materials. These cycle every half hour I think. So for each basic facility you have set up, every half hour you need to make sure you have 3000 units of your basic raw materials in storage / launchpad (Base Metals, Noble Metals, Heavy Metals, Non-CS Crystals).
Step 2: Advanced Industry Facility takes 40 units of 2 different types of processed material and turns it into 5 refined commodities. This has a cycle time of 1 hour meaning one basic industry facility per raw material should feed this continuously (don't connect them directly though, route through a launchpad).
Step 3: Advanced Industry Facility takes 10 units of both your refined commodities and turns it into 3 units of robotics. Again cycle time of 1 hour. So to have this running continuously you need to set it up like so:
--------------------------------------------------------------------
Raw mat 1-->Basic Industry---v
Raw mat 2-->Basic Industry--->Advanced (Mech. Parts)
^ x2 (remember route each process into the launchpad, NОT thе next industry facility)
Raw mat 3-->Basic Industry--->Advanced (Cons. Electronics)
Raw mat 4-->Basic Industry---^
^ x2
Launchpad (Cons. Electronics & Mech. Parts) ---> Advanced (robotics)
This will keep your robotics factory running.