I didn't use bibs at all in the first 3 months, just muslins. I guess the other items really depend on how often you expect to do your washing. I would allow for 3 changes a day on average, maybe only 2 if not too sicky but up to 4 or 5 if you have a leaky baby! So if you wash a couple of times a week then prob about 8 or 9 vests, long and short sleeved, just to be on the safe side.
I liked to put my kids in outfits so they had quite a few of these that they wore during the day, then sleepsuits at night. I had prob about 5 or 6 sleepsuits. A lot of people prefer the baby to just wear sleepsuits for the first few weeks as they do spend most of the time sleeping, so if you do this you may need a few more.
Don't forget you will prob get lots of presents too so maybe hold off getting too much initially. Also, I don't know if you are team green or not. We didn't find out the sex for babies number 1 and 2 and I found once they were born I didn't want them to wear anything white cos I wanted everyone to see she they were girls. So some stuff that I bought barely got touched.