You'll get your uniforms fitted within the first week and although you'll get them straight away (unless you need alterations), you won't wear them until service training (about 4-5 weeks in like Dan said).
Rochelle, I would recommend attending. The hourly rate is very good, and the minimum number of hours you should get is 80 a month, but from what I understand you will get much more than that. I'm almost finished training and everyone I've met along the way from MAM have been very happy with the hours and money. I have met a number of ex MAMers who are now CSMs or on the 380 long haul, so career progression is there. Qantas flies all over Australia so there are a variety of routes (you will get decent overnights!), and as short haul you will operate on some international routes too.