buckworks - 6:22 pm on Mar 27, 2010 (gmt 0)
70,000+ pages is a lot of pages to add ... my concern would be whether the site has enough Page Rank strength to support that many pages effectively.
My opinion would be to add the new pages whenever they're ready, but move cautiously in terms of how you link to them from the rest of the site. You want to give the new sections enough links to make sure the spiders can find them, but you wouldn't want to spread your Page Rank too thin too fast.
Be sure to support the new content with some new link development.