Well, I'll hazard a guess some on this site might say things like "Don't mention girl friend/fiancee" or they will tell you to lie. This is bad advice IMO.

My advice, since you asked, (and which is free so worth what you paid for it) is to be honest but don't volunteer a bunch of extra information.

A simple example would be: Someone asks me "Is it your birthday today"- I could answer "yes" which is true, or "yes, and I am having a big party". The party is extra information which can open a door to more questions like where, when ,how many guests, etc.

It is always good to have some documentation linking you back to your home country (Australia). Some of which you might have produced at the Emb/Cons where you got the B visa. Examples Bills, pay stubs, property records, etc.

Will you be working with the Australian gov't while in the US? (Embassy or Consulates) and if so do you have appointment letters or documents. That could be handy too.

Frankly as with any immigration encounter it could be a quick couple of questions and a goodbye, or a secondary where US contacts are telephoned.
That doesn't help you too much I am sure, but I always go with the short but true answers with a smile, or at least not a growl.

Good luck.

P.S. 70 minutes will be cutting it close at DFW. I would also prep yourself for quick a TSA rescreen which you will have after immigration and customs. have your liquids in the baggy, computer out, belt off.

EDIT- I presume you are an Aussie BTW, but even if not the same would apply to my advice.