I agree with Christy, take one step at a time.
As it will be your first full term/successful pregnancy, who knows what your last few weeks will be like? You might swell up like a real melon belly momma (I love your ticker!) at 30 weeks....you never know.
I don't think you're being unreasonable wanting to take a break earlier, and go back to work later. It's easy to make assumptions now when all is well, but I'm sure a lot of your DH's opinions will change as time goes on and parenthood hits!
Putting an infant into childcare at 6 months just so you have some play money isn't a half decent reason (in my humble opinion!) either.......but obviously it's up to your and your DH.
Sounds like your DH thinks you're a bit of a wonder woman (with your full time working and studying) and if he's the part time worker, I hope he's serving you like a husband should and cooking/cleaning etc.!!
It's a good thing you're both discussing your options so early on....very sensible!
Hope you have a most fantastic, healthy pregnancy!