I don't think you should allow folks to "strategize" by not answering the K or D questions. As set up, I could answer questions all four days and avoid the hardest questions each day.
If the goal is a "contest", then contestants should be able to take advantage of the rules, etc.
But if the goal is to create a WOC output that is valuable to subscribers and reward those for participation, then make everyone answer every question they get. Otherwise, the K and D rankings will be subpar and we don't get the WOC on the real hard decisions each week. It also reduces the skill involved (the better contestant can figure out Ks as well as QBs).
I also liked the 50 questions a week to get more data for the rankings. It didn't take much time. Go with your gut.
The rules should also have some factor for rewarding for more questions answered. Again, this inentivizes more data for the WOC rankings.