Cache strategy for big site?

Hello,

We will host a quite big website (about 50.000 articles) and 2 millions comments. About 20 new articles are posted all together at a specific time, once a day.
There are between 60000 and 100000 pages views every day.

On each post page we display the last articles by widget. In each article there are links to the author page and to the category page (though we can remove). We also display a RSS feed that is updated once a day, and best of that we update once a day too.

I don’t know which cache strategy to use: Caching the whole website with metas takes a few days (currently 4800 posts in 9 hours)!

Of course 90% of visitors read the most recent articles, though older articles are sometimes read too. Author and category pages are also read and if they aren’t cached, take a few seconds to show up.

Which strategy could you recommend for the best result?

Thank you!