The prefix 'great' is used to differenciate the island of Britain from the French region of Bretagne or Brittany. The prefix is only meant to refer to the size of the island.
Conquest, murder, birth or marriage.There has been no conquest since 1066 (except the interregnum of 1649-1660, but nobody became King on account of it).Murder may have happened in advance of Richard...
In 1707, the Acts of Union brought together England and Wales with Scotland making Great, (or Greater), Britain. Great Britain isn't a country. It's the island that England, Scotland and Wales share....
Prince Charles is currently first in line. It is unlikely that he will take the position, due to his age, so it's more likely that his son, Prince William, will be next.