I've read that it's usually easier for the older child to adjust to not being "the baby" anymore when there is a smaller age gap. This was true in my family; my brother and I are only 16 months apart, and we were best buddies until we got to school age and saw that we could have friends of our own gender, but even after that we still played together quite a lot. Whereas my younger brother is 4 years older than my younger sister, and apparently he spent most of their childhoods teasing and tormenting her, and he remembers being extremely jealous of her in the first few years, for taking away his baby status. But then, we are all friends now as adults, so I guess it doesn't matter much in the long run.
I can hardly imagine going through pregnancy while having a small child to take care of, but lots of people do it, and I plan on trying again when this one is between 1 and 2. I'm just hoping my next pregnancy won't be as exhausting as this one is.