How to do internal and external link building on internal pages

i want to know are actions below increase or decrease SEO and my ranking in Google ?

is it good to use a plugin for internal link building or do it manually ?

how many internal links i can set to an article ?

how many outgoing links can i set per 500 word article ?..and what if the outgoing link is dofollow ? dose it reduce my ranking in search engines ?

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