A review article is nothing but a literature review. Unlike an original research article, a review article is a survey and evaluation of already published artcile. It is the most intricate thing while writing a dissertation. When it comes to the number of articles to be included, it depends on the subject or the topic of the article and your knowledge of the respective topics. On a rough gauge, it can anywhere fall between approximately 5 - 20 published papers.
If you want to know more about literature review; you can refer to this blog which explains everything about literature review:
A-Z of literature review - https://typeset.io/resources/the-ultimate-guide-to-writing-a-good-literature-review/