I have a larger chest as well and throughout my pregnancy my bra size changed 3 times, and then one more increase after the baby came. At my largest I was an F cup! During pregnancy, I looked for regular bras that were inexpensive. I knew that they might mot fit in a month or two and be in the store again looking for a larger size. I would not recommend bra extenders which only increase the band. Your cup size will most likely change and you will want to be comfortable. You might want to look into a maternity bra only because of your chest size. from what I understand, maternity bras provide even more support and comfort for large busts, but I had no problem with regular bras.
As for nursing bras, it really plans on what you plan on doing while breastfeeding. For sleeping, I would STRONGLY recommend staying away from the sleep bras at motherhood. The cups are just cotton crossover and they provide no support. When I would lay on my side to sleep, I would spill out because the bra would not stay in place. However, these bras were comfortable to wear around the house (again no support so they were not flattering in clothes, but still very comfortable). I liked to sleep in no wire cotton bras that they sell at wallmart in two packs. They were still all cotton, but had some shape to the bra so the cups stayed in place. These also make great everyday around the house bras.
If you plan on going out or having lots of company, I would recommend having at least one under-wire bra to wear so you feel like your breasts are in the right place, and everything appears smooth under your blouse. I ended up wearing an F cup and target did not carry my size, but motherhood seemed to work well. I noticed some other posts praising target and putting down motherhood, but in my experience there were no problems.