So, here it is (but please note this is an early plan and has since been modified a bit):
The layout is in two levels: the upper level will feature the yard at Narrabri West on the "long wall", and the "downtown" section of Narrabri on the "window wall," separated by a pile trestle across the Namoi river. Two rural "silo towns" are on the lower level, Gurley, along the window wall, and Edgeroi. The two levels are connected by a 26" radius, four-level spiral (i.e. "helix"), with a gradient of around 2.25%. Staging will be in an adjacent bedroom, two five-track staging yards stacked atop each other. The Walgett branch will be represented by a short branch to "Wee Wa", which I'm undecided upon whether to put inside the adjacent bedroom or on the remaining wall. I'd really like to keep this wall free of layout, as eventually it'll be occupied by a flat-screen telly.
Operations will be centered at Narrabri West. This terminal has a through mainline and parallel passing loop; trains can also be "marshalled" on two running tracks along the back side of the yard; two stub-end storage tracks are provided as well. The terminal is typically NSWGR: a two-road locomotive shed is provided (the prototype had three tracks), and the loco depot also features a 60' Sellers manual turntable. Out-of goods traffic is handled at a standard goods shed and loading bank. Livestock are loaded on a "sale yard track", and inbound shipments of fertilizer and bulk oil are recieved on private spurs.
One big feature of Narrabri West is the large grain sub-terminal which will rest atop the spiral to the lower level: carloads of grains from rural elevators (Wee Wa, Gurley and Edgeroi) will come here for storage, and outbound trains of grain for the port of Newcastle will be loaded outbound.
An important element of the depot will be the ancillary structures the railway provided for operations: a 12-room crew hotel and "refreshment room" will need to be scratchbuilt, as will several smaller buildings like the crew showers, chargeman's office and the like at the loco depot. These buildings will emphasize the Australian setting of the railway.
Next up: Let's get building this thing.