Ali you are a mindreader! Seriously! DP and I have only been discussing this very topic this evening. I went back and looked at some old threads earlier tonight - there seems to be a wide variety of opinion/experience. Here is a summary of what I have read (hopefully the memory is holding up!):

1) Size 0000 or 000. It seems to be almost impossible to predict which would be most appropriate before the baby is born. Someone said they left the 0000 in the packets with the receipt docket just in case for ease of exchange. Others said they only had a few 0000 and then had someone go out and buy more if they were needed. Weight seems to have some influence but it is probably more to do with the length of your baby or how tall he/she is as to what size is required. It's better to be too big than too snug.
2) Depends on the hospital - some will provide all clothing for baby and you only have to take a going home outfit, others require you to bring in all clothes for the duration of your stay. (Give yours a call to check). Some mums preferred to put their babies in their own stuff they had washed etc themselves, even if the hospital was supplying stuff.
3) Two to three outfits per day was the general consensus but take heaps of wraps and using a bib can reduce the frequency of clothes changes. The other advice which seemed practical was to have seperate tops and bottoms for baby so if there was a leaky nappy, it only required a half change

I hope that helps! I came to the conclusion that it is impossible to predict (like everything else after that first labour contraction) and that it might be better to have a minimum of stuff and then send DP out for more once we know what we need. We are thinking of giving instructions to family and friends not to buy below a 0 and that we will take care of the really newborn clothes to make sure we don't get swamped with too much gear that will hardly be worn.