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. If you have someone you can call, invite him or her over to play with your two-year-old so you can get some rest or sleep. You'll be surprised how much a 15-30 minute nap can help you get through the rest of the day.
It is also important that you sleep when the children do go down together, especially in the evenings. It is tempting to stay up in the early months so that you can have time to yourself or with your partner, but it is very important to keep up on your rest so that you can be the best woman, partner, and mother you can be. Be gentle with yourself and all the rest will fall into place.