Re: If you didn't BF your first...
There are still benefits for older children--immunological and nutritional ones, particularly. My 4.5 year old is still nursing and I think it is still very good for her. But one thing--he might not be interested in breast milk because it tastes different from other "milks" he may be used to. I had the opposite situation: my DD wouldn't drink any kind of milk or milk-like substance except breast milk until just recently.
If you're going to pump for your older child, you need to establish a supply for your baby, so I would focus on learning as much as you can about nursing before baby is born. Start going to LLL meetings when you are pregnant, read as much as you can (The Womanly Art of Breastfeeding, Dr. Jack Newman's Ultimate Guide to Breastfeeding Questions, The Nursing Mother's Companion, Dr. Sears' Breastfeeding Book, plus many others), watch videos of good latch, etc.
Good luck! I know of several moms who have struggled to nurse their first but had great success with later babies.
Catherine, mama to Preschooler Girl 9/08, Toddler Boy 3/11, and Twin Girls 2/14!