a) The General consensus is that UNSW is better, but quite honestly, UTS is moving up and you really can't go wrong if you have good extra-curriculars/experience etc.
b) From what I've heard, you need an 80 WAM. And apparently it's not quite hard if you knuckle down and really try your guts out...
First off, I don't think getting an atar high enough means that you should do the course. Do what feels right. I know a friend that did UMAT for fun, got in the 95th or so percentile, got 99.9 ATAR and is still doing Engineering which the cut-off is about 91. Since this decision reallly is going...