They are definitely their own persons! I have three and as much as they are similar they are so different. Linda7NJ mentioned in one post how easy her baby was -- that's how my 3rd was, and I am sooooooooo grateful -- my first was colicky, my 2nd wouldn't go to anyone but me, and while my 3rd favored me, he was mellow and slept well and ate well and had a good disposition.... and I'm SO grateful since the oldest two were still preschoolers and there was so much "other stuff" going on in our lives at the time.
As far as sleeping & verbalizing when they were younger, they were all different and their individual patterns follow them to this day -- but even my youngest (who could fall asleep in 2-3 min) would startle, wake, and make noise if something about his environment changed within the first few minutes.
JMO and just my own experiences