John i'm not as mad keen as some but do get out after geese a bit, the time of year depends on how much water is still around in other areas, last season there was apparently still heaps of water on the plains out kakadu way and the birds stayed out there longer, and didn't realy show up in numbers until nearly the end of the season, the mango crop draws them in too.
Harrison dam, Lambells lagoon and shoal bay reserve are the only public areas and are pretty good anyway with lots of people filling thier bag limits.
Its either an early morning or just on dark affair as this is when they are either leaving or returning to the swamp, evenings can be hectic but you run out of light real quick so the window is short, I prefer mornings as you can get the early flights but if you hang around you will still get some stragglers and ducks comming through, just gives you some more time.
As for retriving them you try to sit back far enough so they drop on land, if you have a dog you can send him in, you see blokes trudging around in the water but I would rather stay out of any water more than calf deep.
Its all steel shot only and in BB or No1.
Blokes do use decoys but as I said I'm not that mad keen.
As for the fishing, barra generally slow down a bit during the cooler months and start to get a bit more active as the build up starts warming up but as Ben said you can catch them all year just not as easlily, theres plenty of other good species in the salt(most as good or better eating than barra)and tides are more important than the time of the year or day, If you go on a charter they know where to be on what tides and generally do pretty well.

cheers Gaff