Your main page should be full of keywords because that page has a higher chance of being indexed than other pages. And for some search engines, it will be the only page that is indexed.
Some engines will rank your page highly if it has at least 100 words on it, so consider that your minimum. Directories include pages based on the quality of their content, so make sure your pages aren’t just lists of keywords. If you do that, you risk not getting in the big directories AND you will irritate readers they wont come back.