Hi Cessna,
From Spring (starting yesterday over here on September 1) through to December is ideal. It tends to get a little warmer in Summer time here so from December to late February-March it may get pretty tough when you dig targets and the temperatures are soaring. Usually there's a lot of flies about in late October when they can get out of hand... you can wear a fly net or buy some repellent in a can. Most prospecting supply stores tend to carry some here. Try to get some strong stuff because our bush flies are far more persistent than city flies. It's not unusual to have more than 600 flies on you when they reach plague proportions and bush flies don't move when you swat at them. Ticks are usually only a problem closer to the coast or further North of the state. Snakes are out in these months but they're very timid. You can bring some snake gaiters with you or buy some on Ebay if it makes you feel a little safer. To my knowledge, no Prospector has been bitten whilst detecting but a few of us have had coils snapped at. A bigger, heavier pick will help you dig deeper holes faster but if you are visiting from overseas, buy one here... don't bother flying one in. Might be worth joining up with a Prospecting tour here as they may be able to take you out with them and show you the more remote locations etc. Most people here will be very helpful towards out of town visitors.
Cheers,
Marco