HI Heather,
I have 2 children; a five year old daughter and 4 year old son. We always knew we wanted to have more than one child, and because we waited to start having kids, we didn't really have time to ponder how long to wait between the two. I am really glad we had them close together. They are very close friends and love to play together. However...
The early years of having kids close together are really hard. Be prepared to be sleep deprived. While I totally think it's worth it to have them close together, I know that without being a strong person and without a supportive partner it can take it's toll. You have to be willing to give up some things to make it through and give what you need to the kids. For example if you are a person who likes to have an immaculate house and cook every night, you probably won't be able to do that. You'll have to realize that you just can't do it all. Later when they are a little older you get to go back to those things.
Here are the great parts though... when they are close together, they typically will nap for at least a year on the same schedule. This is a really nice break to be able to have. You don't feel like you're "starting over" because they are just naturally developing right after each other, and I think because they are so close in age you are able to more easily include them both in the same activities, so no one feels left out.
I also have a boy and a girl. I don't know if this matters, but it feels like they don't compete for the same things in the same ways. They like some of the same things, but not all and that little difference seems to lessen the conflicts. BUT I also think it really depends on the kids and how you and your husband parent to establish that relationship and dynamic.
I also run a home daycare and see lots of little ones who adjust to being older brothers and sisters, and I'd be happy to talk to you generally about examples of those situations and personalities.
I would say to take some time and think about what's best for you and your family. I have one daycare family who are terrific parents and they are stopping at one child. When I asked why, the mom said that they know their limits and that there are other things that they want to do which would be harder if they had more than one child. I think there's a lot of pressure to have more than one child, but I don't think that's always best for all families.
It's good to ask for other people's experience. At least you'll have some idea of what you might expect! Good luck!