I have heard great things about Overland Park--many friends have delivered there. I also needed a level III NICU and delivered at St. Luke's on the Plaza (they're actually a level IIIb--a little more advanced than a III). My son had to be transferred to Children's Mercy soon after birth and I wanted to be as close as possible. Their NICU was great for the short time he was in it (they intubated him and started him on prostin--for heart).
If your child has to be moved to Children's Mercy, s/he is in excellent hands! As far as a pediatrician, ask your OB. You'll probably want one that specializes in critical care.
Best of Luck! Babies are so strong:)