Having just gained approval for a self-prepared I-140 NIW petition, I have collected a few after-thoughts (while my mind is still fresh), which I hope will be of value to those who may comtemplate to go through the process on their own.
1. If you have excellent records of achievements (eg, patents and publications) and decent command of English language, it may be a good idea to petition by yourself. Your chance of getting approved will be good even without the help of a lawyer, as long as you focus on the issues that have been outlined by NYSDT case (see www.twmlaw.com).
2. Collect and present as much evidence as possible. Try to highlight your achievements in relation to the national interest and scope as well as intrinsic merit of your petition.
3. References shall also center on the issues mentioned above.
4. As for RFE, although up to 12 weeks are given for a reply, it is prefereable to respond as soon as possible (the advantage of DIY is obvious under the circumstance).
5. Timewise, a self-prepared petition may take about two weeks.
6. As a test for your command of English language, if you can write a reasonably polished manuscript within two weeks of being given the experimental results, you will be ok to petition on your own. Otherwise, it is better for you to seek assistance for your NIW petition.
Good luck!