We have 3 children, and their age differences are 23 months and 18 months. I now have a almost 4.5yo, almost 2.5yo, and 11 mo. It is awesome!!! Now there are times that are seriously challenging and frustrating, but WAY more times that are sweet and very funny. My first two are girls, and they play together all the time and chatter together all the time. The conversations they have are so wonderful and often very funny. My baby is a boy, and his older sisters love to play peek-a-boo, chase, and generally boss him around. He ADORES them! When he and I go to pick the girls up from pre-school, he starts screaming with excitement to see them.
The 23 month age difference was really great. My daughter was really loving and nurturing, and sometimes too rough. I chose to discipline her only for intent, and just try to be careful about the rough hugs and pokes. (I said lots of things like, "I love how you're hugging your sister, but can you tickle her toes?") Anyway, once my second daughter was a little sturdier at about 3 months, I didn't have to be so careful and things got a lot easier. I always kept pacifiers and blankets in a place that she could reach, so if I ever needed to have her leave for a minute, I could ask her to help by getting me one. (She LOVED to help!)
I can tell you that the 18 month age difference was really challenging, especially for the first few months of my son's life. My 18mo daughter didn't understand taking turns on mommy's lap, and would often get upset when I had to nurse him. She had a hard time understanding what I meant by 'gentle', and I really felt bad having to let her be upset so I could take care of the baby. One real plus was how quickly my son could join in their play. However, that difficult time was really only a couple months, and then it got much easier.
All that being said, I imagine no matter what the age difference is, there is a period of adjustment and challenge. I suspect that it always takes a few months to get used to your expanded family, and managing the challenges that having a newborn brings. I have found that my capacities have grown as my family has grown. In many ways, I feel more relaxed and at ease with my 3 kids than I did when I had one.
Good luck to you during this exciting time. You sound like a natural mom, and I'm sure whenever you decide to have another baby, you guys will do great!