Queen Elizabeth's successor

[Torrain]

That's confirmed. William has become Duke of Cornwall and Cambridge. Cornwall was one of his father's titles that was deactivated when he became King.

The title of Duke of Cornwall passes immediately to the monarch's eldest living son. The title of Prince of Wales is bestowed at the discretion of the monarch, not automatically. We can expect William to be made Prince of Wales probably after the mourning period and Charles' coronation to give him his moment in the spotlight.

I fully expect Prince Harry and Meaghan Markle to lose their last remaining royal title (Duke and Duchess of Sussex, respectively) in short order, assuming they don't give it up themselves. 

I’m not sure about that - it would risk making Charles a highly political figure from day one (assumption at the moment is that he’ll try and tamp down his strong opinions for the time being).

If anyone is getting their title revoked, it’s the Duke of York.

[Torrain]

Why is there a 'Prince and Princess of Wales' royal title (and designated heir to the throne), but not an equivalent for Scotland?  I know 'Prince and Princess of Scotland' sounds strange at first, but I am sure it that novelty will wear off over time. 

As Lord Halifax notes, Wales was a principality, and so was ruled by a Prince. After England and Wales were unified into a single kingdom, the title of Prince of Wales was revived as a title subservient to the King of England & Wales.

When the England and Scottish crowns were unified, the two kingdoms were ruled as one. William, as heir to the British crown, does hold the title of Prince and Steward of Scotland, but this is subsidiary to his other Scottish titles, most notably Duke of Rothesay, and the much cooler Lord of the Isles, which comes from a 12th-15th century domain comprised of the Hebridean Isles, that mostly fell under the MacDonald lordship: