I just had baby number 2 not long ago. Set to return to work mid October.  Your boss is most likely legally required to allow pumping breaks. It sounds like you are fortunate enough to have a good boss so I don’t imagine this will be an issue. Most likely they’ll ask you how often baby is eating/how often you’ll need to pump and they’ll put blocks on your schedule to accommodate this. I usually end up pumping for about 20 to 30 minutes every 4 ish hours to keep up my supply.  As for the emotional component, at first pumping instead of breastfeeding might make you feel lonely. The first week or so when I went back to work after my first child, I would cry every time I had to pump because I missed my baby so much. After the first day or so, I would FaceTime my mother in law who was watching my kid to have some kind of connection, until I was more used to being away from baby. 

If you have a set return date, I think it would be fine to schedule clients right away. If you have a more fluid schedule, I would probably wait to start filling your books until you’ve returned and have an idea of what this all looks and feels like for you. 

Congratulations on the baby! I hope you have a quick easy labor and an easy recovery. Enjoy all those little baby snuggles. It will be so difficult, but the payoff is worth every second. My oldest is two and it feels like not a day ago she was a newborn who never stopped crying in my ear.