The quote for the ticket is around £1400 + taxes, so I guess it'll be economy class? (definately not first class!)

Just phoned up Qantas and was told that if the ticket is open dated then every time a flight is booked the ticket will need to be changed to include the date and for that there'll be a fee of £10, which can be charged but will depend on the mood of the person at the time (her words, not mine).

She also said that if I buy an open date ticket then I can't reserve any flights until after I've set off, which sounds crazy (I'd literally be trying to get my next flight for 8 days after I'd set off). More confused than ever now.