Hi Stevey
You're spoilt for choice really. I also like cars and moutain biking.
We live in Berwick about 45mins east of Melbourne CBD and its ideal.
I go MTB'g 3x a week at Lysterfield Lake Park (hosts a variety of MTB events including the Commonwealth Games MTB in 2006)- its excellent. You also have the You Yangs on the West side of the city for more extreme tracks, Mount Buller and alike about 2 or 3 hours north for full on downhill MTB'g. The weather here is ideal for MTB'g. Not humid. It does rain a bit in winter but that just keeps the trails from drying out to dust. In summer it can get seriously hot compared to other cities but just means you have to go earlier in the morning
We have the Formula 1 obviously, two rounds of the V8 Supercars, MotoGP and World Superbikes at Philip Island (1.5 hours south).
4x4...... The entire continent is your playground.
Melbourne is definitely a sport oriented city, so put it on your itinery.
The beaches are good - in the bay there's no fear of sharks. The surf beaches are more attractive and of course the higher up Australia you go the warmer the water gets which is why the crocs & jelly fish like it so much.
Your trade is brilliant and gives you the opportunity to chose any city that you like. Good luck with that choice.
PM me if you come over and want to go for that bike ride