Hi Marius,
Average temp in march at Bandya WA is 30.5 which isn't too bad. Even on days up to 37 you can still squeeze in a good few hours. I normally get out by 5.30am and pull the pin at 1 or 2 pm.
If you have experience and are prepared to put in the leg work an oz a week is about average.
Seriously, I'd love to help you but I can't guarantee weather or things popping up here on the station wouldn't interfere with your plans.
Tour groups usually don't start hitting the area until about April, and realistically no tour group or person can guarantee you'll find gold. They can guarantee they'll put you in the best position to, but that's about it.
Try sending a message to Kris Dobbie from Coolgardie. Lovely lady, very experienced and capable operator and tour guide
Cheers.
... it's nothing you "just buy" 
