hi pink kitty,
1) you can straight away buy S size.. In fact, dont even need to buy too many bags.. I KS bought many bags of S n Newborn size and even bought 1 bag as spare at my parents' place but end up wasted I gave them away.
so from personal experience, buy diapers one bag at a time and for starters, S is good enough
2) The hopsital nursery has clothes for babies but on discharge you need to dress up your own baby. I had a "going home" outfit for my baby upon discharge. I let him wear a tiny romper, plus a receiving blanket to swaddle him, and a little beanie for his head.
3) Sorry cant answer this Qn cos I had C-section under GA as my baby was breech and my waters broke suddenly before due date and I had to have an emergency C-section