I always wanted kids, wasn't sure how many, had a notion that twins would be nice, then had dd1 and was eternally grateful she wasn't twins! I recall after dd1 was born I was at a postnatal group talking about how many kids we all wanted, some wanted to stop, I knew I wanted more, probably 3 in total. As for how you cope, that worried me too, but it wasn't so bad, we had 20mths between first and second, and the baby thing is considerably easier second time around, because you've done it all before, some things will be different because the babies are all different, but essential stuff like how to breastfeed, change a nappy, burp them, and the confidence to leave them to whinge long enough for you to get dressed - all that will make the baby part much easier. I found a small gap was useful as I quickly got baby into a routine of napping at the same time as toddler, so we all 3 of us had a rest! No such luck when we had dd3 (age gap of 19mths after dd2), as eldest (then 3yr4mth) was no longer napping, so that was a bit more tiring. Again I wondered how I would cope but it was like when I had dd2, except now I had a 3 year old who was very keen to be like mummy and help mummy. Also the older two played with eachother while I sorted out the baby, so in many ways having the third was easier than having the second.
As for the fourth, well she kind of fitted in around all the existing chaos! She came along when dd1 was 5.5yrs and was on the school run at about 8 days old (and we were there on time, the whole tribe - very impressive given that I could barely get myself dressed before midday at that stage with dd1!).
So here I am with 4 girls, and one husband with the snip!