Maternity Shoot Help!

So I didn't have maternity pictures done with my son 8 years ago, and never planned on getting any done with this pregnancy. But today I got a surprise. My best friend contacted her sister who does photography and gifted me a free maternity shoot. I'm so excited and keep crying. Anyway, I need advice. At what week do most women get these pics done? I'm 32 weeks today. Also, what do you suggest wearing to show off the bump? I seen some beautiful dresses on this site that cover the breast but open up to the belly. Where can I find these? Any advice please!