Yes, we are in the same situation. I think my colostrum came in a few weeks ago. My daughter will be 3 in August and she was also super excited. I had similar questions about how it would work for changing to regular milk so I asked my friend who is a LLL leader. I will just copy what she said so you have the information too.
Lactogenesis I, the first stage of lactation, when colostrum is made, begins midway through pregnancy. The breasts are already primed to begin secreting this magical fluid. During the first half of pregnancy, estrogen prompts the ductal system to proliferate and grow. Progesterone is responsible for the increase in size of the lobes, lobules, and alveoli. The breasts become larger and veins may be seen through the skin’s surface. As these changes take place, the areola becomes larger and darker; the nipples become more erect. The Montgomery glands under the areola also enlarge. The breasts then begin their secretory phase, filling the alveoli with colostrum. The breasts become more distended and heavier, preparing for breastfeeding. Lactogenesis I continues until the mother’s milk comes in (Riordon 2005).
After the delivery of the placenta, Lactogenesis II begins. The sudden drop in progesterone triggers this stage of lactation. The new mother will start to produce mature milk within three to five days. The milk continues to be a mix of colostrum and mature milk for up to two weeks postpartum, through the transitional milk stage.