My point wasn't the closeness to the throne or otherwise of the Norfolks, but, rather, that many of the 'suitable' young women who William might meet could well be Catholic, i.e. it doesn't necessarily follow that if William finds a British woman whom he wants to wed that she'll be a Protestant.
The 1701 Act of Settlement prohibits any Catholic from becoming King or Queen, or marrying the heir to the throne. If William did indeed wish to marry a Catholic, whether she was British or not, he could, but he'd have to relinquish his place in the succession.