Her name will be Catherine Mountbatten-Windsor. that is prince Williams surname . though royals usually never go by their surnames that's his surname and they use it for important documents such as marriage licenses, etc.
The Royals usually don´t have a last name but if they ever use it would probably be WINDSOR-MOUNTBATEN
Yes.
Windsor is their surname. Their titles will be Prince and Princess of Wales.
She will be known as Catherine of Wales or Catherine of Windsor.
She could be HRHPrincess William, but she seems to go just by the DUCHESS OF CAMBRIDGE.
Windsor
Kate Middleton will become a princess when she marries Prince William. If William becomes king, Kate would then become queen. If Queen Elizabeth II abdicates the throne to Prince Harry however, Kate will remain a princess. This would seem unlikely considering William is in line to the throne before Harry.
No, Kate will be called Her Royal Highness Princess of Whales. That or longer. The royal family does not take the last name from Bride.
Windsor
If he dies without children, Kate will be the dowager (whatever her former title was). And then Harry and his line will succeed to the throne. However, if William dies before he marries Kate, then Kate gets no title at all.
William is 28 and Kate is 29
Prince William will marry Kate Middleton.
The Best Man at the Royal Wedding of Prince William & Kate Middleton was Prince Harry, Prince William's brother.