I would definitely start working at a Level II NICU. You will get the basics of what neonatal nursing entails. You need a good background and experience working with infants who are less ill, so that you know what is "normal" behavior, vital signs, and activity patterns in a neonate who is stable, vs. going right in and starting to care for critical infants.
Caring for critical infants is intense, labor-heavy, and can be exhausting. You are caring for sicker infants, and will not have time to study why certain procedures are done, drips started, care restricted in particular ways, or why certain medications are given. It is doing one task after another, quickly, while monitoring the infant's vital signs and how he is reacting to what is being done to him. Observing changes in his overall state, some of which may be small and seemingly insignificant, takes practice. You will get that practice and experience working in a Level II NICU. You will learn to care not just for your baby, but to offer support and guidance to his family as well.
Remember, too, that babies in Level II NICUs may suddenly become sicker. As you gain experience and knowledge, it will help you to detect changes in a baby's condition earlier, so you can see how an infant reacts when he is first decompensating or getting sicker, & can act appropriately. You will learn why certain things are done to a neonate, vs. only learning a list of tasks associated with care.
It would help you a lot to have an understanding of pathophysiology, anatomy & normal behaviors associated with a particular gestational age. You will learn time management skills, multi-tasking, and delegation. These are all skills that you will take with you throughout your career.
You will need experience in a Level III NICU before applying for NICU flight training. Different hospitals have different requirements. In our hospital you needed a minimum of 2 years Level III nursing before applying to be a flight nurse.
Good luck in your nursing career!