The most important thing I learnt from my first ATB many years ago is to eat and drink all the time. Eat every 3/4hr-1hr and drink plenty along the way. Otherwise you will struggle on the second half and eat like mad for days after it's over. You probably won't feel hungry so force yourself to eat, ...
My training is year round.
Daily commutes to and from work plus club rides each Sunday.
Buy good clothes and wear plenty of layers in the cold weather, just keep riding. Even in winter the Melbourne days can be great for riding if you have the right clothing.