1. because although the packs give you 100% of your RDA vitamin and mineral wise, you simply would not be gettting enough calories to fully breastfeed. I would assume, having done it. There may be other medical reasons too.
2. Possibly be able to to do the diet but probably not on sole source (where you have no normal food at all)
3 I did the diet this spring and if you are less than 5,8 then about £36 a week, if you are taller (or a man) then around £48 a week
4. I would say the steps are designed to do 2 things, 1. introduce food in a controlled way and 2. keep buying the diet for as long as possible. I didnt do all the 6 steps as they reccommend, which would have taken months. I introduced a meal at a time over the period of about 3-4 weeks and so did my husband.