Prefolds are the way to go.... you use them when bub is newborn and then reuse them as for extra boosting in pockets ect down the track. Prefolds can be used upto 3 months plus. Using them for this time frame will give you the opportunity to see what shape your baby is, wether they are long and skinny, built like a rugby player ect. All nappies are different and fit a baby differnetly.

I personally am not a fan of OSFM. I just find they outstretch and dont suit every baby type. I also didnt like that most are made of PUL outter which dont allow babies bub to breath fully and caused nappy rash for my kids.

Baby beehind fitted are good to have. start with a 6 pack and see how you go. Wool covers allow for breathing as do fleece and minkee

Id say a good Newborn stash to start with would be 24 prefolds or terry flats and 5 covers to routate. Maybe an AIO or 2 for the nappy bag when your out and to show off

oh and as someone said before hand...flussable liners make a difference