While it depends a lot where you will be working and/or if you're willing to commute to the CBD (central business district) everyday for work.
Where you will end up living will also depend on your price range of renting or buying. Obviously living within a few KM's radius of the city centre, you'll expect to pay a lot more than if you were to live in the same sort of place 15 KM out from the city.
I live in the inner Southside of Brisbane, my high school was in the city centre, so I have plenty of friends that live all around Brisbane and I learnt quickly the best places for schools, transport and roads (freeways etc). I would look at houses within a 4-10 km radius from the CBD. That is where you'll get the best public transport options to get to and from the city, as well as a more "reasonable" housing costs.
We really don't have decent beaches in Brisbane, unless you go out to the Bay which is really just play beaches for children... no real surf and sand type thing.
We do have a free public man-made beach called South Bank, there are some great fish n chip shops/cafes/restaurants in the South Bank vicinity.
If you're after a "real beach", about an hour south from Brisbane city you have the Gold Coast. And likewise about an hour north from Bris city is the Sunshine coast.
Be prepared that the weather will be very very different to Ireland. My father is from Scotland and it took him a little time to adjust to the much hotter climate. We have hot Summers, so make friends with your neighbours who have their own pools (there are also various public pools around the suburbs for which you will pay about $4+ for one adult entry!).
There are plenty of social groups in which you could join as families. While I'm not completely sure of specific Irish or German clubs, there are plenty of adult/christian/church groups, as well as youth groups for the children. We have various Scout/Girl Guides centres around Brisbane, also check out the PCYC website for young people. http://www.outdoorsqueensland.com.au/01_cms/details.asp?ID=220
This website has a list of groups for different age groups, and social demographics http://www.brisbanecitylife.com.au/bcl/intgroup/social.htm.
I would also take a look at www.realestate.com.au. It can give you a realistic idea of suburb demographics and what you can expect to pay from suburb to suburb.