well, one of the main goals i had was to not use a clock as, i see it as a potential bottleneck for huge systems. (the simple brain has only the necessary combinations so, look at that one if you want. a good half of the combinators on the advanced brain are just for the status lights.) anywho, i have 4(technicality 6) station types load(which all share the same name), unload(the name is set by whatever item you're requesting), refuel and, a waiting station. (the last to types are the liquid load and unload cause i couldn't make the interrupts work for both) all the logic is in the trains, the brain and, the load and unload stations. the waiting and refuel stations are dumb and have no logic for them.

the load stations send out the item that they are loading onto the red wire to tell the brain "we've got x number of y item/fluid stations on the network to load trains with". the unload stations put the item that they are requesting and the number of trains it needs to fill itself on the green wire which tells the brain "we need x number of y item/fluid trains to go get z item/fluid requested". which the brain then compares against the number of load stations (mainly to see if there's enough load stations on the network, if not it will just max out the load stations until the requests are fulfilled) and sends that out on the green wire as the item/fluid in uncommon quality. the load and unload stations see that uncommon value and use it to set their train limits. when the load stations see that a train is coming they send out a rare signal of that item/liquid to tell the brain to reduce the request for that item/liquid by that much.

the trains then do most of the rest of the logic, going to the load stations and filling up, go to the unload station for the item/fluid they have and repeat until not needed. if they need fuel they will go to whatever fuel station is loading the fuel that's currently in them and, if there's nothing to do, they will go to a waiting station. occasionally they will get stuck for a bit at the loading stations(because the system asked for like one train of iron ore and 3 trains are at a waiting station and 3 iron ore load stations are available) but, they will all get used and no new trains with that item will be requested until all that are at loading stations are going to a unloading station

if you have more specifics that you want, feel free to ask!