This looks to be a pretty impressive build. I've known guys working in N that did more compression than you in their mills. If I were to do a furnace, I KNOW mine would have to be compressed, as I'd want to do Dorothy 6 at the USS Duquesne works. Used to see her lighting up the night from my grandparents porch and drove by her daily for a couple of years.
I admit to skimming a bit, so I missed if you have any plans for deliveries/shipments off layout? Is that what the tunnel on the left side is for?