I have 3 young children. My daughter is 5 1/2, my son is 14 monthes younger (she was 5 monthes old when I got pregnant with him!), and my third child came 23 monthes after him. Although it can be CRAZY I have loved every minute of it. They fight like cats and dogs sometimes, but then when I see them or hear them playing so nice together it still to this day warms my heart. They are each others best friends. Now not to say that siblings further apart can't be that close, but when they are that close they seem to have more in common. This coming year my daughter will be in kindergarten, my son in his second year of preschool. The year after she will be in first, he in kindergarten, and my youngest in preschool. It just flows so well! And you don't forget what you've learned from the previous!
Good luck in which ever way you choose to go, either way, having two is awesome! Hope this has given you a little insight.