Hello Seymour, and welcome to the forums. Sorry your excellent post went without a reply for so long.
You asked several questions, and they do fall into several possible forums. But each question would benefit from actual testing and research, rather than opinion, so this may indeed be a good place (even if quieter) to take on all those issues in one thread.
I've done some research with pagination, scrolling and so on. In my study, there was a sweet spot - we found optimium page views when scrolling was at around 4-5 screens worth of scrolling per page. Fewer than that and the visitors did not go as far into the content, on average. More than that and they abandoned the content sooner as well.
While this study was not done over many sites, it seemed that users neither want to click "too much" nor did they want to scroll "too much". But we are no longer in the era of "I don't want to scroll at all".
The study was not looking at ad display - and clearly a lot will depend on whether you are getting paid by the impression or by the clickthrough.
I'd say a lot depends on the goals for this change. Usability can often work AGAINST ad clicks - people who are "into" the content are not as likely to leave by clicking on an ad.
There may be no answer ahead of time for you - you may need to take some baseline measures and then try out various changes.