The movies are, in fact, entirely unreleated to the series, I would think, as the first movie has told a different story (though same general plot) to the anime.
Death note is based off a manga that's already been completed, and is sticking quite true to the manga, so far, so it won't be ongoing, and, as hostghost said, it's planned for 37 episodes. Manga-wise, they're up to about...volume 3 so far, with episode 10, and half way through the volume at that, so I'd say it's perhaps about 4 episodes per volume, give or take.
12 volumes, so that makes it 36 episodes. Basic maths, but it's a good estimate *oddly proud of self*