I have a SEO Problem. Can anyone clear this for me?

I have a wordpress blog up and running. But now I want to make another one. I have selected some keywords to target but the thing is, I don't know whether to target them to pages or posts.

Like, I can target my keywords to separate pages or separate posts. But in terms of SEO what is better?
Is the category-pages going to be regarded "duplicate content" as they are under two urls? (the main blog post url and the url under category).

Now search engine robots consider on html page to be on page. So what happens to he blog's main page where there are a lot of posts? Like each post is targeted to a different key word. So interms of SEO the main page will be ineffective right?

Can anyone clear these problems?

Each post of a wordpress blog has its own separate url and each post is treated like a different page. The single post page of every post has its own specific url.
Search engines nowadays are very smart and so are the CMS systems like wordpress. To avoid the duplication issue, the areas of a wordpress blog that can arise the problem and made noindex by default and hence they are not allowed to be indexed by search engines and no duplicacy issues arise.
I would also like to say something about the home page of blog. I am not an expert of SEO but by my experience I can tell that thousands of blogs are up and running and they perform very well in search engines. Some even perform better than comparative websites. So it means that there is no problem with home page of the blogs. May be wordpress or google itself have developed some means of avoiding any issues with the home page of blogs.

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