Our best advice is to try not to worry in advance. It's good to anticipate and seek strategies, but the secret to parenting is being flexible and going with the flow. Parenting is unpredictable, so the more flexible you are, the more relaxed you'll be. Enjoy getting to know your newborn, and when he is sleeping you can give your older son some individual attention. If you find yourself becoming exhausted, call in reinforcements. A mother's helper (or a teenager or trusted friend) can be of tremendous help during the early weeks.
First, you might have a very different experience with your second baby -- you may find that you are more relaxed, and that both of you sleep better at night. If the baby is in close proximity, and you can meet her needs without too much disruption, you might get a better night's sleep than you had with your first. It's best to keep an open, positive attitude, but, at the same time, prepare ahead!
