yes of course lets say you have 50 000 pages each page with different title and content this is huge potential comparing to website which have 5 pages
There are many theories behind this one, but in general I would say this isn't really a huge determining factor in rank.
More indexed pages the more internal links you can use target to you main keyword pages and you can also build contextual links. Which will help with some non-external ranking factors.
more indexed pages will eventually lead to more internal links, so more links pointing to homepage and also more keywords can be targeted from the inner pages