I have gone through my newborn and 0-3 month stuff... I have 5 nb outfits, 5 sleepsuits and 2 vests. I have also bought a nb coming home outfit (thought a new one would be nice for this baby rather than having ALL hand me downs!). I have a lot more 0-3month (Ethan was also 8lb 10oz so looking at a 9lber this time eek!!!) and have bought a couple of extra bits but its mainly going to be 3-6 mth stuff that I will need due to the difference in seasons at that stage.
As you say, if you need smaller you can always go out and get some.
ds 9/4/09, Forever missing a baby boy xxx bump due 14/8/11