Hi J.,
We have 4 children, with the oldest age 6. They're all less than 2 years apart. While it's sometimes chaotic and crazy, we are very happy with our group. It's such an individual choice, but adding another little one to your family has so many positives. Our older three just adore their little brother, and I love watching them help feed him, pick out his clothes, play with him, etc. Having kids close together does result in some bickering, and for me that's the hardest thing to deal with, but they're also so close and get along pretty well. As far as expenses go, we've been able to hand down so many things, and get lots of "gently used" clothes from friends, so besides the cost of food, we haven't noticed much of an increase in the household expenses. The first 6 months after a baby is, of course, somewhat exhausting, but it does settle down.
It's hard to know what would be the right thing for you to do, since each family is so different, but I've found that having a number of kids is, overall, a wonderful thing.