Hi Guys - I have been here 13 years after arriving at age 21! Advice I would give is as follows:
1. Have a look for house shares in New Farm or other suburbs that are pretty close to the city - generally the nightlife centres around town. Try http://www.realestate.com.au for shares and renting.
2. Like people have said before - seek is the biggest job site here and throughout Oz.
3. You won't "get it" til you arrive and have a look around but distances are big! I'd say that marine jobs would be centred on the coasts and they will be fewer in Brissy, whereas business jobs will be fewer on the coasts! It might be easier to get a marine job on the gold coast say, a business job in brissy and live somewhere on the train line half way between!
4. I assume that you are staying at the YHA on Upper Roma Street? Near to there is a decent supermarket (Coles), Suncorp Stadium (get yourself to a Broncos game) and some decent restaurants / pubs. Roma Street station is about 500m walk which is the main transit centre for Brisbane City. You can get the "Airtrain" from the airport to Roma Street for about 16 bucks each which is definitely cheaper than a cab.
5. Get yourself a "Go Card" to use the public transport - it makes buses, trains (except the Airtrain), ferries and city cats (catamarans that go up the river) far cheaper (you just scan on and off etc - like Oyster card in London).
6. Start off small job wise - get into the waitressing and deliveries / labouring (you shold find a job no probs I reckon) then just keep looking for other stuff.
Hope this helps - good luck and enjoy the weather - it is perfect at the moment!! best time of the year!!