There is an v8 https://factorioprints.com/view/-N1Fjabs3MgcG7obW_E_
Each wagon has its own request and its slots filtered. the request is reduced by the amount allready available in the train. then its is filtered by the availability in the network. so the filter inserters only try to input thing available. when the inserters has
when there is no filter present other inserters set to black list item loading into the train remove them from the requester and put them back into the network by active providers
trash wagon is emptied with stack inserters into active providers
fuel wagon is loaded fast because the buffer chest next to the wagon hold a wagon full of each tier each of the 4 requester requests just 2 stacks of the needed fuel if ther not enough high tier fuel available the request is set to the lower tier as well.
on the base the lower tier of fuel is removed from the requester when a higher tier is present. on the outpost it works the same but also the lower tier is stopped being requested aswell.
the content of the train is put on the green wire connected so the outpost is only enabled when it is low on any item that is also available in the train.
it is also put in a memory cell so the outpost does not switch of if the train is out of the station.
in the outpost the request are also filtered by the content in the train so the inserters are not stuck on none available items.
in the outpost you can set items you dont want to turn up as trash (like iron ore in the mine, or plates near the smelter)
if you read untill here thanks for the effort. i tried to write it so enybody can understand it. If your busy with it for a long time it seams easy.
the stations consyst of modular parts and im am still making the blueprint look nice.
Credits: White list filter by Halke1986 on the r/technicalfactorio memory cell by by jaideep on the factorio forum