Train "Queue" System

[megaspeeder]

I am currently trying to create a system in which various trains arrive at a train depot and unload their contents, then these contents either wait or are passed onto a main bus. This main bus then goes into furnaces and returns as the smelted ore. Once smelted, it goes to a different train depot and depending on what the type of ore that the main bus is transporting, it will activate a split-off and deactivate the rest of the main bus ahead. That way, it "opens" a circuit from the ore unloading station to the ore loading station. The thing is I'd like to control which ore stations are activated and deactivated with a queue system, which will add a train's content to a queue system to then be processed in the order of arrival. Any thoughts?

P.S: My setup looks like this:
https://imgur.com/a/T8JaZQJ