If you look upon it as an adventure then it will be just fine. Dont burn any of your bridges if you can possibly help it and keep the options open to go home if you dont like it.
You are going to be in a very different situation from families which emigrate together because in a mixed nationality relationship, you will be the one on your own and dont underestimate the isolation that that can cause. I would advise you not to settle too close to his family - that can be quite difficult and I have certainly resented the fact that DH has his mob closer than mine is over the years. Whilst it may seem that they will be a support, and that is a possibility, there is also the possibility that you will be the outsider in all regards and that can be a problem with respect to children etc (another board I frequent has a prime example of a mixed marriage falling apart and one partner being totally isolated versus the whole family of the partner) - so if they are in Victoria, aim for NSW or the other side of Vic (at least 4 hours IMHO

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If you can twist his arm, get a cast iron agreement that if you dont like it he will go home with you. Whatever you do, make active decisions about where you go with your life rather than just going with the flow so that if your opportunities seem better back in UK then you make the decision to go.
It will be devastating for your family, of course it will, and no skyping, msn-ing or emailing is going to make up for that but hopefully they will understand that it is something you want to do. Perhaps your parents could do what my parents did in their retirement and come here for 6 months (summer of course!!!) every year - mine did it for 15 years and so saw my boys growing up.
There is IMHO nothing inherently "better" about Australia, it is just another place to live your life in and your life is absolutely what you make it. If your DH is keen to go "home" now, imagine how you may get the same feelings down the track - just be sure to acknowledge them and make decisions accordingly. As long as you dont feel pressured or trapped in Aus then you will be just fine. Have a ball!