My advise would be to get a few small baby and newborn items but only a few until you know the weight. I had such a time of it as newborn in 1 shop is tiny compared to newborn in another. Ethan was 8lb 10oz when he was born so although some of the newborn stuff was still huge on him, most of it went unworn and there is about £500 worth of items in a box to be sold, infact less as I gave a whole load away.
Although ethan was a big baby, he wasn't chunky he was like a spring chicken but he was very long so I found petite newborn fit him in width but the length was too short so we had to go to newborn where items were like sacks but fit in length. We had quite a limited wardrobe and still do have problems with the length of clothes on him. No matter what age you'll find sich a vast difference in size from one place to another.
It will save you money in the long run. I'd get those packs of 4 or 5 bibs, 1 in each size, a few babygrows in each size and outerwear i.e. a pramsuit in newborn and that's about it at the moment.