The authors own personal research could be summarised as follows
How Many: it is a very rare name, it seems to have spread from the area of Cromar in Aberdeenshire and less so, from Fife. There are a variety of spellings which would all sound similar in English/ Scots/ Gaelic. They immigrated to English colonies. Using a number of dubious methodologies it is estimated there are (4-5k?) globally
Where from: mostly from the area of Cromar and more broadly Aberdeenshire, particularly down towards Balmoral and West to Tomintoul and Granttown. There was also a family of some prominence in Fife.
Notables: there are few aristocrats - certainly no Princes or Dukes, a couple of knights, and most notable one predominant family from a farm or landholding called Auchtercoul and now known as Westercoul in Cromar, Aberdeenshire. It is uncanny in the research that when a Coutts "achiever" is found they always seems to relate to this family.
Auchtercoul Coutts: include Provosts (Mayors) or Arbroath, Montrose and Edinburgh in Scotland, the Heritable Usher of the Black Rod of Scotland, North American and Baltic trade pioneers and the banking family.
Thomas Coutts: was a billionaire banker in todays dollars. He was a an early partner of the Coutts Bank, aka Coutts & Co, aka Coutts, he died leaving his second wife and 3 daughters.
The aristocratic English: not surprisingly Thomas 3 daughters were found very attractive and married into the aristocracy who changed their name by licence to include the name Coutts. One of his grand daughters, Angela, inheirited the bulk of his fortune and became the worlds greatest philanthropist and was made the first Baroness (and famously created a huge scandal marrying her private secretary 30? years her junior)*
Coutts Bank, aka Coutts & Co, aka Coutts
A highly respected Private Bank established over 300 years ago. It is said the Royal Family bank with Coutts. As expected they have very stringent banking criteria.
Fame: Sir Russell Coutts KNZ is arguably the greatest sailor of the 21st Century.
* this is dealt with elsewhere but is worth repeating. The various wills of Thomas and his second wife stipulated conditions around the inheiritance. One was the 3 girls must retain the name Coutts and another that they could not marry a foreigner. This was made by Thomas' widow as she was horrifed when a grandaughter (?) married the grandson of Prince Lucien Bonaparte (and this was not that long after the Napoleonic wars). Angelas' husband was American and her family were very angry about the embarrassing age difference and her sister sued her for breach of the Will and won X% (or that's my summary at least)