how many keywords are perfect for website ?

As long as your main keywords are in the URL, Meta title and a few places in the content that is all that really matters. Its also best to keep your keyword density low (1% and lower is a good general rule of thumb)

 

First, your signature looks spammy in an SEO forum. Remove those as they are not relevant and may look spammy in Google's eyes.
As for the keywords, I like to use one keyword for one article. However, I do support it with several related words. The keyword should be repeated at least once in 100-150 words. If you will use more than 5 keywords, you can calculate the math. It is going to look absurd. I mean what will you write if you will only target 5 "giant" keywords in your content? And then we blame Google for penalizing our sites

Anyway, are you writing content for your gaming website? Or just mentioning those keywords in the description?

 

You should work on at least 3 commercial keywords and 3 non-commercial keywords for one web page. You should also create links on the URLs of the web page. This is important to have the right backlink profile with relevant keywords.

 

There's no limit to the number of keywords you can optimize your article or page for as long as you keep the number reasonable (e.g. you can optimize for 20 but don't go as high as 200). The benefit of this is that your article or page will rank for more long tail keywords and will send you up to 10 times or more traffic than you would have gotten if you had optimized for just one keyword.

Make sure you include the keywords where they make sense instead of just stuffing your article with them. You can use some of them as headings and discuss them as subtopics within your article.