Did Europe -> Oz with my GF about 4 years ago, we were on the road for 6 months. We went first thru eastern Europe to Turkey, then Iran, Pakistan, India, then shipped to Thailand, then Malaysia, Indonesia, Australia.
When leaving home, we had the carnet sorted well in advance (I think I first contacted the AA here about 6 months prior to departure - but issuing it could surely be handled in a shorter timeframe)... and then we had visas for Iran, Pakistan & India already in our passports, when we set off. We didn´t need visa for Turkey. I think we applied for them just 1-2 months before departure. After leaving India, we only needed visas for Indonesia (at the border, BUT do check, as they may not issue them at every border!) and Oz, which was just an ´electronic´ one, and could be handled on the web.
But you´ll also need to be aware, that visas depend on your nationality. Your foreign embassy will know those things. And also note the different visa types, and how long they´ll be valid.
From what I´ve read here, it seems that regards the paperwork, the route to India thru the Stans could be a little more complicated than our route. And it also means you´ll need to cross into China, which is complicated and costly, but apparently possible, and requires contacting the travel agencies in China several months before the planned crossing. It´s been widely discussed here at the HUBB.
Here´s more from our trip:
MOTO1 - Matkalla