How many keywords should I use on a page? I want to target as many keywords as possible to attract a lot of traffic, yet still have high search engine rankings.

One.
You should have a (more) general keyword for your home page, and more specific keywords for the other pages. If every page links to every page, the subpages should get ranking for your main keyword too.

It depends on the number of word on that page . You should use keywords in the density of 4-6% .

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