Hello friends,

How many keywords is good for SEO..?

Depends on whether you want good SEO or Great SEO. Best practices would be 1 long-tail keyword (2-3 words long).

It depends on your web pages. and depends on your target. actually on long tail keyword is prove very beneficial for the best seo of any website.

That depends on how many pages you have up on your website. And the market you want to target with your website. For small businesses, I often suggest 5 keywords or so. And once their websites appear on Google's first page on these 5 keywords, then can integrate more keywords in their SEO keywords basket.