I raise horses, not dogs, but the time commitment is very similar.
At first, I had to have someone else do all the horse chores. My midwife makes the new moms do nothing but nurse and rest for the first two weeks, and she won't clear anyone for exercise (even walking) until 6 weeks. After that, I carried the baby in a sling while mucking stalls, leading horses to and from the field, and doing a little grooming on the quieter horses. I even stacked hay wearing him one day (I can't really recommend that!). When it was cold, I wore a very big coat I could zip up over him. There is also a really cool poncho for sling-wearing moms called the Aiska poncho. It's pricey, but well worth it.
Hubby or a friend or family member should walk the dog during the day at first (and you should have some help around the house for that time frame anyway! Then, see how you feel from there. You may have to adjust the dog's schedule a bit and take the dog out when someone is around to watch the baby for a few minutes, and hubby may have to take over longer walks.
A three year old dog should be able to adjust well. A few things to keep in mind (I'm sure you know this already, but here's my standard tale to clients expecting a new baby):
--NEVER leave a baby or child alone with a dog or cat, even if they seem to get along. The baby could make a sudden movement or sound and scare the pet into doing something harmful or dangerous. Once the kid is walking, the kid could hurt the pet on accident. [My mom left my sister alone with my grandmother's dog, who licked the baby, and the baby had a bad allergic reaction right there, at 2 months old. So it's not just for bite prevention.]
--Introduce them slowly and carefully, and expect the pet to have some degree of anxiety. [our four cats freaked out -- we didn't see two of them for 2-3 days, and I was getting very worried about them, as cats that don't eat are at risk for liver failure.]
--Work on a dog's leash training before the baby comes. You may need that dog to be very responsive to you, in case you drop the leash or need the dog to stay.
--Let a pet smell something from the baby, if possible, before bringing the baby home.
--Come inside the house first, especially if you were at the hospital for a few days, and greet your pet for a few minutes before hubby brings the baby in so the pet can get the excitement over with.
--Ask your vet for any information on introducing a baby to the family they might have. [I used to give out a packet of information when I had my own clinic, but not every vet does. The clinic I work at right now doesn't.]