You have to do it while you are still "insane". Sane people don't have children, on in my case, adopt.
And if you want more than one, they need to be less than 5 years apart. If you get one through bottles, diapers, and daycare before the second one is born, then you'll realize how crazy your life has been and you won't want to do it again.
When I agreed to adoption, I had cold sweats every night for a week because I couldn't imagine being a father. After she was born and came home with us, I couldn't imagine not being a father.
Every once in a while I see a cute baby and think "I'd like another one." Then a couple days later I see a 3 year old getting on its parent's last nerve and I think "No chance in hell am I doing that again."
Heck, if you can, have them about 2 years apart. My boys are 21 months apart and it's cool to see how much closer they are than I am with my siblings. I am the oldest and my brother and I are 4 years apart. I am almost 7 years older than my little sister. When my wife and I started having kids, I told her that there was no way I was going to have kids that far apart.
As far "starting over" again, my wife and I sort of had to do that with our daughter (3 mos. yesterday). She had a really easy time getting pregnant with our boys. We had decided that with 2 boys, we'd give it one last shot to see if we could get lucky and have a girl. We started trying and just like the boys, she was pregnant right off the bat. Except this time, she had what the doctors called a "passed pregnancy" which is basically a miscarriage without the egg ever implanting. After that, conception was a struggle and it really wore on my wife and started to harm our marriage.
Eventually, we decided to stop trying in about January of last year. In the meantime, our then 2 year old took to potty training quickly and by March we were done with all of the baby stuff (and still not pregnant). We were done with diapers, bottles, pack and plays, cribs, etc. It took us a while, but we had really accepted and embraced "only" being a family of 4. So much so that my wife decided to have a bunion removed on her foot that was really bugging her. That was her real "acceptance" with not having another kid because she always said that she would wait until we were done.
So last June, she had the surgery. About a week later, she tells me that she hadn't "started" yet. At first we thought it might have been the stress from the surgery (or the drugs). She tells me the same thing a few days later and I told her that it she maybe should take a test. Next morning, she does and there are two lines. Bam, we have another kiddo on the way after getting rid of all of our baby stuff.
But we got our little girl and she is beautiful, happy, and healthy (which is all that matters).