I have three, the older two were 4 and 3 when the youngest was born.
I won't lie, is was hard! I found it a much bigger jump than from 1 to 2. It's much more expensive. As they grow, there are many more arguments and bickering than there would be with 2. There's mess, chaos and noise all the time.
BUT, I wouldn't change if for the world. It's amazing. They rowed quite a lot when younger, but now they are 20, 19 and 16, and great friends (and have been for a few years). They find each other funny, love each others company, and we are all really close.
However, I was lucky that they are all NT, and both DH and I have jobs that can be flexible, so we never had to pay for childcare, and we were able to run them round to various activities/school runs without too much trouble. When they were babies, DH would get up in the night, or stay up late to do the last feed so I could get enough sleep. DH was around quite a bit in the day as well if needed. I might think differently if that hadn't been the case.
Ultimately though, the biological need for me to have a third overruled any doubts I had. I didn't get the urge for a fourth!