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 DropOffGreenElectronics, the train would leave the yard, or sometimes 2-3 as at the time I didn't have any way of limiting it and one train wasn't enough to service all of the delivery points with my single car trains. the thundering herd problem[1] was real. the first train would get there, rest would go home. everything refueled at the home terminal, which had a stop for the coal train on it. each train had (dropoff(X) -> pickup(X) -> rest(X)) for their instructions. it worked pretty well.
Interesting approach. I do give multiple pickup points for the same name (so while my old coal field is slowly running out, trains increasingly move to the new coal field by themselves), but I hadn't considered doing the same with the drop-offs.
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.
Newer versions of factorio have a per-station limit on the number of trains that can be in + routing to that particular stop. very helpful for this kind of problem.
I always make them refuel at one of their regular stops. There's usually a source of fuel nearby, so I just route a small part of that along all the engines.
But sometimes I forget, and sometimes there's no fuel nearby.
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.