Our third was a surprise. The age gap is not large it just wasn't a planned third. After getting over our shock I found no. 3 easy as her birth and early months she was the calmest, most easy going and chilled out baby. She has remained our "easiest" child and we could not imagine our family without her or her older siblings.
It has turned out there is a reason I found dd2 easier, as my older two have now been diagnosed with HF ASD. At the time she was born ds was 4 and starting school, dd1 was 2 1/2 and their social communication issues were yet to be understood.
Practically speaking we were fortunate to be in a four bed house already, there is a financial impact and it is more difficult to find cheap holiday accommodation etc. Really it depends on what your priorities are, how you define a 'good life'.
With 3 under 5, life was pretty intense. Now they are 8, 11 and 13 things are easier but I am preparing for the next few years when we will have a period of constant exam preparation, ds will be entering y9 tomorrow. When ds is doing GCSEs, dd2 will be doing SATs , when dd1 is doing GCSEs ds will be doing A levels and so on.
Three sets of uniforms three different schools to deal with (from tomorrow), three hungry teens to feed (in just over 4 years dd2 will be 13). But I regret nothing they are fantastic kids.