Cairns is a great place to live. Has some of the 'big city life' as in places to eat and things to do. Its also small enough to be a bit of a country town if thats more your style. Best of both worlds.
Jobs wise you will need at least 500 multi and a couple of renewals to jag charter work. Skytrans is the biggest GA RPT operator there and is doing alot of hiring lately. Aerotropics also have a big operation. Hinterland is another good operator up there. There is a bit of aeroclub instructing done there but the training in Cairns has dropped down in the last couple of years.
Horn Island is pretty much the place were most Cairns pilots cut their teeth. Living up there is basic and its hard work. Some are lucky to do rotation rosters in and out of the place but most get stuck up there working for fairly poor $$$ whilst working hard. Good character building stuff. *cough*
All big operators up there do RPT so if you want a job get up your planned IFR and night hours. Fairly high minimums also due to RPT requirements. But I think there are one or two single operators up there if you have lower time. Its hard to tell what info you want as you didnt supply much!
Get used to paying through the nose for descent food or "kai kai" as shipping is expensive. Take some good books and adopt a camp dog like most other pilots up there. Be prepared to catch some interesting tropical diseases and fungi. If its anything like when I was there your liver will also be punished. You will have a great time if you can do without life's luxuries.
Good luck. Big esso blo yupla.