I'm on a 457 and the only thing I can add to the comments above is in regard to health care for dependants. My daughter required a filling and a brace for her teeth which I could no longer postpone. The whole thing has cost me nearly $7000 and I will only be able to claim back about $2000 from my company health insurance.
The company insurance also didn't cover eye tests for her etc etc. Before you leave make sure the policies cover everyone travelling and you've had all your checks on the NHS!
Good luck with it.
PS Interesting comment that GP bulk billing is only for kids. I've used it a couple of times and not been charged.