Other people might comment on details point by point but here is my 2 cents:

I applied through a lawyer (wegreened.com). NIW is a long process to get everything ready. One of the main thing that I learned in this process is how to present your case. I have read people who had over hundreds of citation and did self petition and got rejected. The main reason being they couldn't put a convincing case to the USCIS officer. Recommendation letters are very important for this purpose. The letters are not like regular letter. It has to be written in a way so that USCIS can't point a finger. This is done by avoiding any vague words (such as, may, shall etc).

Just think about the letters and cover letters as a legal document, for example, you are lawyer and you are presenting a case to the judge. We have all seen from the news that what a good lawyers can do.

Most of the lawyers write the letters and cover letter. Like with wegreed.com, you have to provide a summary of contribution and based on that, they draft the letters and you can revise as many times as you want until you are satisfied. The letters has to be written in such a way that layman can understand. And also having a versatile list of recommenders help.