School and breastfeeding can be challenging when the baby is very very young. If at all possible, I would try to get more time away after you have the baby- one week just isn't enough time to recover physically and for both of you to get good at breastfeeding, especially since you've never done it before. Most lactation consultants don't recommend introducing a bottle before 3 or 4 weeks.
The principal seems supportive- is there a way you could work from home to try to keep up at least a little bit after the baby is born?
That said, I was unable to take more than a week off from school when my youngest was born (3 months ago); my husband came with me and got me when the baby needed to nurse. After three weeks, babe stayed home with a bottle and I pumped every 3 hours. It's doable. It's not pleasant or ideal, but it's doable.