I’m sorry but your idea of a central distribution hub just won’t work in Train-Fever as it does in the real world. Movement of goods must not take more than 20min from supplier factory to user city overall (20min rule is absolute). Distribution hubs will not work in the game unless the distances involved are very small. I know, I tried them when I first started playing the game!
The 20min rule is one of the most frustrating issues in the game that urgently needs revision, it makes some sense with passengers, but it makes no sense at all with non-perishable goods. The rule for goods needs revision!
I’ve found that small dedicated freight lines working: commodity producer > processor > city terminal, is the system that works best in the game. These are best kept completely separate from your passenger network. Slow freight trains do no mix with faster passenger trains, as is true in the real world.
You need to make sure all your cities have 100% of their goods requirement satisfied to allow them to grow. Without this your game will not develop!