whats the smallest block in that area?

Berwick is very overrated and expensive, considering you want to move to Berwick, it will be much better if you move to a closer suburb. ie; Rowville, Endeavour Hills or Patterson Lakes. But if you want to stay within the area, I'd highly recommend Clyde North or Beaconsfield. Don't live in Berwick save your money and buy a house in Clyde North or Beaconsfield.