Difficult to say without hearing you speak. I know many people who say "my English is bad, I can't speak", but when you hear them, often, they are not as bad as they thought. I have found that it is mainly a confidence issue, people believe their English is bad when in fact it isn't. All you need is to find someone to practice with before you go...:-)

Can you survive in Australia with you current level of English? If so, do not worry about that. I think you will be motivated to use English there, so your English will improve somehow. It could be also funny to speak language like Tarzan does: "Tarzan good boy. Tarzan strong and fly.":D

http://esl.about.com/od/grammarintermediate/a/cm_good.htm

Grammar mistake:  Good vs. Well

Good* tends to be used when using a "Form of Be" (is, are, was, were, might be, being, been, am).

Also

Is* it necessary.

If the job is very professional/high level, then maybe take classes on Italki.

Else, save your money and learn on the job.  Post in the Notebook area here and let people correct your grammar.  Learn from the errors and corrections.

I think I will spend more time on learning than working if i had such a vacation.

Learning English and benefits your whole life.

If I have vacation time

I will go to learn language is more than I like English

Will also learn other languages