These are good questions. I don't really have answers to them, but I do have thoughts that relate to the questions.
Type itself is an approximate concept. But if you believe there is something innate in you when you are born, personality inventories and theories can help you reflect on (and perhaps discover) your innate qualities.
I read that young children tend to be easier to type in terms of the first and last dichotomies: EJ vs EP vs IJ vs IP.
Myers in
Gifts Differing says that healthy individuals differentiate between S and N as well as T and F. She further says they develop primary and secondary function that have opposite attitude (external vs. internal focus), and are opposites in terms of being a judging vs. perceiving function.
Later in life, it seems like the needs of the other functions become more important. Marci Segal seems to encourage the use of all your functions to enhance your creativity. Lenore Thompson suggests first developing your "left-brain" (Te,Fe,Ni,Si) or "right-brain" (Ti, Fi, Ne, Se) functions* depending on your initial preference. John Beebe has a much more complex picture in how the functions affect you throughout life.
*I don't think there is any basis for calling them left-brain or right-brained functions.