We will probably add another row of sleepers... silly me didn't order enough. I ordered them from a sawmill in Epping (which I found on ebay). They only cost $16 each for 2.4m x 75mm thick ones, a pretty good price, methinks!
I can't wait to lay the drainage and fill them with dirt, lay the irrigation and put in lots of beautiful plants... it will be stunning!
Thanks again guys.... you rock!!