Reference letters are key to proving many research based immigration cases. However the reference that Citizenship and Immigration Service (CIS) likes is not the same type one would get to obtain a job. The major thing that CIS is interested in, is the opinion of scientists in the field.
The CIS does not care about big names in the field. The Government would be barred by 14th amendment, to give more credence to someone from say Harvard, rather than say Podunkhollow University. Yet scientist very often want to get so so references from big names in the field, rather than good reference from not so well known scientist. CIS officers are NOT scientists. They just want a scientist in the field. Their credentials are meant to just qualify them to speak on the issue. It is more important what they say, rather than who they are.
The CIS does not care if you are hard working, diligent, easy to get along with. They are not paying you to work, nor are they working with you. The referees must prove the points of the law.
The referees need to say:
1. Why your work is important in their field
2. Why you are better than the average researchers in your field
3. How your research will help the US as a whole
Usually disinterested referees are the best, those people who are not your friends, or co-workers, but know you only professionally and are familiar with your work, rather than with you.
There is no magic number of references, but I usually go for 10.
Conclude by saying why the referee thinks that labor certification will be a laborious process that might hinder the research progress.