Hadn't thought about whether odd or even numbers were better
I think I'll stick with 4 for now, (if in doubt, choose the cheaper option ), since it is an ongoing line with a large store (Harvey and Norman), I can always order a 5th one if 4 just doesn't look enough, they have a delivery time of 3 - 4 weeks so I'm sure it won't hurt me to wait a few weeks if I decide on another one after we get the 4 in place.