I have established that NPC null systems are going to be a very low volume market. Extremely preliminary data indicates that average returns could be vaguely in the range of 5% per month, at which rate an investment of 10ish billion isk only returns 500 million. That is not a lot of money, so if I'm going to do this I need to reduce the effort involved to practically nothing.
In theory I can interact with my trade hub/s as little as once every 90 days - that being the time that it takes for sell orders to expire - and that should probably be my goal. The process might look something like this:
1. Stock a system.
2. If you run out of an item, double the number you keep on market and restock.
3. Repeat #2 until you go upward of 90 days without restocking.
4. Every 89 days minimum, adjust orders by 0.01 isk to reset the expiration timer.
If I were end up using that method, it would be really convenient if my stocking tool could tell me which items I've run out of. This feature took all of 60 seconds to implement.