Hey Sarah!
Great news about BA!
The pay sounds crap, but it'll get better and quite frankly I'd be taking the job. London is a great place to live and sharing accommodation isn't so bad and BA has a good name (well from a pax perspective anyway). And the Queen flys BA, and I think if its good enough for her......
If ya don't like it, you can always come back to Australia.
Keep in touch and let us know what you decide.