Seo for wordpress plugin will automatically use your post title , content as seo title and seo meta description on new and old posts/pages.
yes . just activate plugin and check all your previously published posts with seositecheckup. I m sure you will be happy with your result.
plugin will automatically copy your post title as your meta title content , first 156 charachter of your post content will be used as your meta description and post tags as your meta keywords.