I have baught bits and pieces from pretty much the start, but waited to get past the first tri to start buying furniture.
I tried to keep in mind that most places will only let you have a layby for 8 - 12 weeks. and sometimes they also have to order the items in, so I guess you don't want bubs rocking up without having a bed to sleep in.

Re Clothes, I will buy one or two things, but most will be kindly provided by family, as they always seem to want to buy little things, So we'll end up with heaps of samll stuf that might not ever even be worn.

Good luck with the shopping though, its great fun