Regarding singlets I found the Bonds 00 was the same size as kmart brand 000 I ended up being given a heap of hand me down singlets too in asstd sizes.
tbh I found that having bubs in a big singlet was okit just came over is bum and didnt ride up. My DS wa 3610g (7lb15). I would buy the kmart or target brand (they seem thicker) - maybe3 or 4 0000 and 6 or 7 000 or if you buy bonds, 4 000 and more 00. You can always use the 00 if you run out. Another thing to consider is the 'cuteness' factor - going into summer, bub may just wear a singlet and nappy some days or no singlet at all under clothes. Bubs look pretty cute full stop so isn't a huge issue.
In my hospital they used a singlet as a beanie - tied the straps/sleeves together and rolled it a bit. The part which usually goes around bubs belly went around the head. Wa a cool thing to do and it saves on them having to have another piece of baby clothing.

Bodysuits - 3 or 4, depends how often you want bub to wear them and will they be used as an outfit? Pumpkin patch online outlet store had some cute ones 2 for $9. Good buy.

Other clothes is hard to say, you will be given a lot. My bubs didn't fit 0000 bonds wondersuits so maybe have a few 000. I did have a few 0000 outfits - about 4 plus wondersuits.
Best piece of advic e I can give is keep the outfits simple - for bubs comfort and eas of dressing/undressing. They sleep lots too and will be wrapped. I know I wouldnt want to sleep in jeans.

Happy shopping