We've been there 5 times, last time about 4 years ago.
Are you going to stay in B.A. or another city? If in B.A. some of the nicer neighborhoods are Recoleto, Barrio Norte and Palermo (the Soho part of Palermo is rather nice.
Getting around B.A. isn't difficult. the Metro is reliable, though limited, there are many bus lines, and taxis are rather inexpensive.
Dining tends to be later than earlier, the earliest being 9pm, and usually later. So if you go into a restaurant at 6pm for dinner, well, good luck finding one open that early. Nightlife is varied, but again, don't expect much action until after midnight or even 1am.
You should have a basic understanding of Spanish. As in any Spanish-speaking country, they have their own unique pronunciation, words and idioms. To me, the accent and cadence sound slightly Italian.
Prices should be cheaper than Australia, but inflation has been running rather high in Argentina for the past few years, and this is coming from our friends who live there.