The hard part about the stay at home working mom thing, as others have said, is that most new babies won't settle into a rhythm of any sort untill they are about 3 or 4 months. And the 2 years after that they will change into a new phase every couple of weeks. So getting into any sort of predictable routine is pretty impossible for the first few years. Most jobs, even the work at home kind, require at least SOME sort of reliable schedule.
Of course, the great part is that you don't miss any of those preciously brief phases either. Also the sense of satisfaction in accomplishing something beyond food, laundry and a shower is very good. Helps to slay the dreaded "baby bubble brain" too.
My last bit of advice is to take a hard look at your budget. Figure out exactly what your weekly TAKE HOME pay is going to be. Then subtract any potential childcare, work expenses, travel costs etc... Don't forget to take into account that your working income might bump you into the next tax bracket. We discovered that, since our insurance and benefits came from my husband's job, I was actually working for less than $10 a day! ugh. Needless to say I didn't work long. We got creative with the finances and squeezed by without my income instead. My girlfriend did this exercise before her first child was born and realized it would actually cost her $$ to work, at least on a part time basis.
It's great that you have options and are thinking about them so carefully. Good luck with the baby!
~ I used to be undecided, but now I'm not so sure ~ Boscoe Pertwee