You need to consider your living budget and plan your prospective trip accordingly . Living on the beaches in Sydney will be very expensive.
I live near Manly on the Northern Beaches and house price, rent/buy , is completely mad, I could buy a French Chateau near my native Monaco. This is one of the many sites you can have a look at for house prices
www.domain.com.au
Given what you describe as the lifestyle you are after , I would suggest you look at Gold Coast (the city) , so much cheaper, no traffic, easy lifestyle.
In the Sydney area, look at maybe Maroubra for more affordable suburb.
Several families I know have left Sydney to move to the Central coast and commute by train. So Avoca, Copacabana, ....
If you want to have a feel of Sydney life, you should look a the suburbs you can afford and stay there and try to see how doable "beach life " is from there. There are no trains to the Northern Beaches , only bus or ferry if you go to manly , you would have to take train+ bus to the Bondi area. Unless you live on the beaches as I do, you won't be doing much beach life during the week , because it is a big city and you don't walk down for a swim after work as you would have to travel for quite a long time.
End of year equals to the Australian long summer holidays and it will be hard to find accomodation if you don't plan it in advance. Everything will fill up pretty quickly.
Holiday wise, I find Noosa and Byron Bay really lovely, probably because they have a European feeling. Water will be warmer as well.
In the south, Jervis bay is nice, but it will be packed at Christmas. Still lovely and great beaches.
As someone from the Mediterranean , I am always amazed at how people seeking the beach life plans on moving to the other part of the world, cruelly far from family and friends, without considering that you have as much if not more beach life in Spain, Greece, Italy, ... You can buy a massive mansion for what you would pay for an average house here. I know you now need a visa for the EU, but so do you for Australia. Water is freezing in Sydney, and we have had two years of very very wet summer.
There are plenty of reason why people move to Australia, but if it is just for the beach, you can make better choices.
There are several discussions on people leaving Australia
Personally , I can't wait for my DH's posting to be over.
Flight prices have skyrocketed as well. Everything is so stupidly expensive,
By all means, come for a holiday at the end of the year, Australia is a lovely country with beautiful landscape, but maybe in June or July, go to Sardinia, Santorini, Mallorca, Menton, ... so you have something to compare it with.
If you need a big city for jobs, Barcelona allows you to do beach life from March till November and between November and March you go skiing at La Molina less than 2 hours form Barcelona. You can live in Gava or Castelldefels in a flat or house right on the beach , 20 min commute by train