Here's a few things to think about
-who's bringing what? [sausages, hamburgers, salads, oil, onion, etc, keep in mind that there will be people with special dietry requirements, such as Islamic fellows who can only consume halal meats]
-entertainment? Last time the BBQ broke up at about 5/6 [when it got dark and cold], decide on when people want to go home, what to do in the meantime, etc [though taking ballgames should be given careful consideration, the yarra is not far from the BBQ, unless you are willing to lose the ball]
-the starting time should be carefully considered, it's january, and probably Aust open, I'm guessing that place would have quite a few people. Who's going early to secure the BBQ [there's only 2], if there are quite a few people, is anyone brining seats/towels?
-drinks?
oh, and one last thing, if it turns out to be a rainy day, the whole thing might be cancelled. If it turns out to be too hot a day, it won't be fun either. planning BBQs are very risky in advance, and generally include a plan B.