Earlier quoted context omitted.
For refueling I've recently been using the cybersyn mod, which let's you easily create a refueling stations that your trains will automatically go to when they're low on fuel (with exactly how "low" they need to be being configurable in the mod settings). I just plop down a refueling station, and a requester station next to it that refuels the refueler and I'm done. Don't have to worry about it again.
My most complex train system had every train carry a single item type, and a large central trainyard. trains won't leave without an active destination. so all of the destinations for dropping off a type had the same name, and similarly the pick ups and would be disabled by circuits if their dropoffs were more than a quarter or so full. so if something needed green electronics, it would activate its DropOffGreenElectr…
And I haven't yet figured out how to disable drop-offs that don't need anything. I often have a single train bring stuff to a couple of drop-offs, but that always feels sloppy. I have to use timeouts on the trains so they don't linger at a station that's too full to empty them. Disabling those stations and giving them all the same name might be a better alternative.