The cut-off is 90, but I have heard that they take people with anything over 85. Although, lately demand has been going up quite a bit so it might not be as low as 85 at the moment.
For Law they are pretty small, like most of my seminars had around 30-40 people in them. With first year Business units, I had around 120 max in a lecture (which is comparatively low) and 25 for tutorials (which is on par with other unis). But once you start your major in second year, that goes down to about 20-30 per seminar (for many accounting units, there are often less than 20 people per unit). I'd imagine that Arts is similar.