On Site SEO Questions

1. 2, primary and secondary.

2. 1-2 % for seed or long tail. About 8% for lsi keywords

* it depends upon your website and content. but you have to maintain keyword density.
*keyword density should be maintain as per google search engine.

2 keywords, one is your primary keyword and other is LSI keyword.

Keyword density will be based on the content you have in the page. If the content is very low, you can add only the target keyword. If you have more content, you can use maximum of 2-3 keywords.

This is based on the content you have in the page. But avoid keyword stuffing.

keyword density is important thing you can maintain 2% or 3%

ex: 500 words content will use 2 or 3 keywords enough

All of these answers, with the exception of gracewilson's, are ridiculous. The answers to your questions are:

1) In most cases, optimize a page around ONE keyword phrase. You have plenty of other pages on a website to optimize around other phrases.

2) Keyword density is a concept that died many years ago, with the advent of Panda and then several other algorithms that did an even better job of parsing content (and/or user behavior) for quality. Your phrase needs to be on your page at least once. That's it. If it happens to appear more than that, great, but it does not matter in terms of ranking for a phrase. Much more important than forcing a phrase onto a page multiple times is getting related phrases (LSI phrases) onto the page and providing something that satisfies a user's query.

3) There is no minimum or maximum number of words. While it is true that the more words there are, the better the content's chances are of ranking for SOMETHING, 2,000 words of crappy content are not as good as 300 words of quality content. User engagement with your content and whether they bounce/pogo-stick back to the search results is the key component as to whether or not your page has enough and the right content. If you feel confident that your content satisfies the search query so well, that they will not have to look anywhere else, you have the right number of words. Rand Fishkin put up a great Whiteboard Friday video about this today - https://moz.com/blog/searcher-task-accomplishment

For home page you should not use more than 20 keywords depend on article size.Keyword density should be 1-2%.use 1500 word of content on your home page

Keywords density is an On Page SEO issue. But maintaining density is not your primary issue. You must use keywords naturally, use keywords those places where it naturally comes.
Unhealthy practice of keywords will be spamming. You can use LSI keywords with your focus keywords. It will be helpful to rank better on Google.
You must use your keywords in the title first and last paragraph, all subheadings, image alt tag and more places.
Just use it naturally, you can maintain 1.5%-2% keywords density.
Thanks, Munna Hossain, Mytechgoal.