Going for a week in April and just happened to notice we will be there for Holy Week and Easter. Any thoughts or possible problems during the stay? Any thoughts re: extras to be seen during that specific time? How much fanfare at the Cathedral during this time?

Are you going to spend all the week in Venice?
As you can see directly from this site (http://www.veniceconnected.com/node/146), April 11, 12 and 13 are the most crowded days, 9, 10 and 14 are considered "middle season" days, no problems before and after.
Peak season days could be like hell in Venice, in middle season you could find some discomforts, especially in the central hours of the day if you are in places such Piazza San Marco or Ponte di Rialto, in low season Venice is simply a paradise.
To avoid big crowds in Easter peak days, you can try to explore the Laguna (Murano, Burano, Torcello), or look for unusual itineraries trying to stay away the most famous attractions, avoiding public boats and use your feet! Venice is bigger than many tourists think, and one of the most beautiful thing to do in it is loosing yourself choosing at every crossroad the less beaten path.