The biggest adjustment you and your wife have made is to the stage of parents. I think you will find that the transition from parents to parents of more than one is not nearly as big a jump as the last.
I totally agree with this statement. Once you get good at raising the first, the second is bound to be a bit less confusing.
I already know what my regret will be. By the time The_Mrs. and I start our brood, we will be old enough that our children will never see us in our prime. We will be on the downside of the slope by the time they are old enough to appreciate us as people rather than parents.
My wife and I have a little boy, not quite 2 years old.
We're planning on 2 more, just have to get the timing down. There were no health issues during the first pregnancy, other than she would experience these brutal cramping episodes a few times a week. Painful, but temporary. (Not the easiest for me to deal with cause all I could do is sit there and watch...)
In both my wife's and my family, we had 2 siblings, she had an older sister by 2 years, and a younger sister by 5 years.
My wife gets along really well with both sisters, they are all bery close, and close with their mom. (Call each other several times a week, if not every day.)
I had an older brother by 2 years, and a younger sister by 2.5 years.
I was closer to my brother when we were little, but by age 10, I began to resent him, he was pretty bossy. (And still is as he pushes 40. lol)
My sister and I always fought as little kids, she would goad m into yelling at, or smacking her and of course go tattle to mom.

I wouldn't say that I dislike my bother and sister, we are very civil when we get together, and it's getting better as we get older. But, I'm not overly upset I live 2000+ miles away from them, because they are both still able to push my buttons if we are together more than a day.
We all have kids now, and I will talk to both of them about once a month or so. Before our kids started showing up, I could easily go a year without talking to either of them, and I wouldn't miss them at all.
Now, I mostly want my son to have a good relationship with his uncles and aunts, and his cousins.
So, to answer the OP's actual question on "timing your kids" so they actually get along, I don't have a clue. :xxrotflma