Happy Chick, I think she started at around 4 months. I would start off with as many words as you can, but just focus mainly on about 4. We started with milk, more, finished & bath, thought taught lots of other words at the same time. Repetition is the key.

With the Auslan site there are different signs as before Auslan came in, the different states used different signs. Auslan was meant to uniform that, though the old sign is still very commonly used. It's not important as to what sign is the right one, what's important is that you stick with one sign for a word. The chances of your LO continuing to sign into childhood is very, very slim so it wouldn't matter if you made up your own sign. HTH