Support every statement you make with evidence. Because this is a research paper, there shouldn’t be any remarks that you make that cannot be supported by facts directly from your research. Supply ample explanations for your research. The opposite of stating opinions without facts is stating facts with no commentary. Although you certainly want to present plenty of evidence, make sure that your paper is uniquely your own by adding commentary in whenever possible.
To draw a parallel, a lawyer researches and reads about many cases and uses them to support their own case. A scientist reads many case studies to support an idea about a scientific principle. In the same way, a history student writing about the Vietnam War might read newspaper articles and books and interview veterans to develop and/or confirm a viewpoint and support it with evidence.
A research paper is an expanded essay that presents your own interpretation or evaluation or argument. When you write an essay, you use everything that you personally know and have thought about a subject. When you write a research paper you build upon what you know about the subject and make a deliberate attempt to find out what experts know. A research paper involves surveying a field of knowledge in order to find the best possible information in that field. And that survey can be orderly and focused, if you know how to approach it. Do not worry--you would not get lost in a sea of sources.
Although it may seem counter-intuitive, writing your introduction first may be more difficult to accomplish than starting with the meat of your paper. Starting by writing the main points (focusing on supporting your thesis) allows you to slightly change and manipulate your ideas and commentary.