Gwiwer,
This is a truly excellent overview of Australian operations for those of us not wholly familiar with the country and the railway operations. I was fortunate enough to spend just over two years living and working in Melbourne and with my very understanding girlfriend got to travel on a great number of the services you mention below, including the full Ghan and Indian Pacific routes, plus Melbourne to Sydney and the Sunlander / tilt services between Brisbane and Cairns. To a lesser extent, I managed some of the routes in rural Victoria and would highly recommend a visit to Echuca, Bendigo and, slightly further south, the Goldfields railway.
If you will permit me and once I receive my personal computer back (it has been on a ship between Australia and the UK since October!), I will post some of the images from my trips. They may not necessarily be of unique interest, but just what I saw travelling around!
My only wish was that I had started to do undertake our exploring earlier in the two years as there are some great journeys out there even on some of the smaller lines.
While it may be uncommon to see your operations modelled, it would seem that there are quite a number of layouts out there. As you say, the Canberra BLT would be a good option, particularly with the preservation yard next to it (and the miniature railway next to that!). I am personally very tempted by a small diorama on my next layout of the junction of the Port Melbourne (ex-Sandridge railway) and St Kilda tram lines with the entrance to Southbank tram depot.
Best regards