Steel Mill problems:
Okay, I think I got it figured out.
Apparently, the problem is - the Steel Mill needs to get Coal and Iron ore in the Mill during the same month. The Steel Mill will accept both products on their own, but it won't make anything out of them unless both products are present at the same time.
Here's how I solved the problem (for me).
I created a station at the Iron Ore source and another station at the Coal source. I created another station between the sources, and created a train with one hopper car.
I ordered the train to pick up a full load of Ore, and to drop it off at the mid point station. I then told it to pick up a full load of Coal, and again, to drop it at the mid-point station.
The Mid Point station has two separate station lines, one right next to the other. One line terminates the source train, the other line terminates the rail to the steel mill. On the Steel Mill Line, I created another train with two hopper cars, and ordered it to wait until full of both Iron Ore and Coal. Once full, I told it to go to the steel mill and unload both cargoes.
At the Steel Mill, I have another parallel double station, which has one line from the midpoint station, and another line that goes to the factory. I created one more train that waits until full of steel, and then takes the steel to the factory to unload.
And voila! The source train makes two trips, and as it drops off resources, the mid train picks them all up (so no loss), and then the mid train drops off Coal and Iron, and the Steel train gets filled up...
Some things I learned (in case anybody else is out in the cold on this):
If your train is long enough to stretch across a road, it will block traffic on that road. (I know, no duh, but I didn't know it until it happened)
It seems to me that you can't change up your consist on your train. If it has hoppers, that's what it has - no way to use the same train, for instance, to pick up resources, pick up steel, and then pick up goods, unless you pull around empty cars on your trip.
Trains can crash into each other. Switches will protect a single rail from crashes, but it also won't let trains move. Building a side by pass for trains to wait seems to work, with signals... but a double track (direction specified by one way signals) or single dedicated tracks seem to work better.
I was actually surprised when I passed the 10%. I'd gotten distracted trying to re-route my road traffic, and bingo, I finally hit.
So - was there somewhere else I could have found the answer I was seeking - or even hints? I searched everywhere I could to find my answers, but had no luck. Is there a secret hidey hole where this stuff is hidden?
I did find a pdf of the Locomotion manual - but it doesn't answer any specific questions as far as I can tell.