I don't know if I've ever seen any research regarding the nutritional value of a pregnant woman's milk. :? I don't see it being tested because they don't like to test much about a pregnant woman, and breastfeeding during pregnancy is still a little taboo.
Normal cycles usually return between 4-6 months postpardem, but it is very normal for a mother's cycle not to return until she has mostly weaned her baby or longer.
My first two are 17 months apart and it is definately not easy. I sure wouldn't change it for the world. Anything younger than that would be beyond my capabilitites as a mom. I am glad Max will be almost 2 when the twins are born, although emotionally that age gap will be harder on him and me, physically he will be capable of more. (Grace was so young she didn't know life without Max and had very little jealousy, although I was still having to carry her around and help her with everything, much like having two babies) It really depends on what type of children you get, which unfortunately we still can't custom order an angel! LOL