To answer your questions…

1. Google Ads were stripped from the study. (the pages went through a proxy).
2. The funding did not come with any conditions.
3. Transactional queries would have also been interesting. But choosing only 2 - navigational and informational still satisfied our primary goals, since they served as a means to separate task kinds, and gave us more data points for each task class.

To answer #4, I was not sure how exactly to interpret it.
You were curious about the fraction of users who clicked the nth link - when? ever? or per query - but users will have different numbers of queries for each question, so we could simplify it to the fraction of users who clicked (as their first click) on the first link on the first query they made, for each question

If you want to know “ever”, or in all queries, including return visits or multiple clicks from a given results page … (and again there is a variation in the number of clicks users make)
then it’s roughly:

rank. percent of users

1. 100%
2. 88%
3. 88%
4. 63%
5. 50%
6. 63%
7. 25%
8. 38%
9. 17%
10. 29%
11. 13%

Thanks again for your interest.