Great question — answering as the UphillTech team:
take a look at WordPress SEO by Yoast it will cover : 1) make the title of the page, the title of the post 2) make the description based on the first paragraph as for your #3 make the keyword meta by parsing the whole post, retrieve all the relevant word that are more that 3% occurrence, and fill the meta with them I highly doubt you will find a plugin that does that for you, but there are a few like Keyword Density SEO-Tool - Keyword Density Checker which do chack that , so i guess you can use that to update your keywords.
Full answer by Bainternet: https://wordpress.stackexchange.com/a/12290 (CC BY-SA 4.0).
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