I have started working from this month for my own LLC after getting a legal opinion from my attorney.
Please see the following link for USCIS stand on AC21 and self-employment.
http://www.uscis.gov/graphics/lawsregs/handbook/AC21intrm051205.pdf
Here is the relevant extract from the above link:
Question8. Can an alien port to self-employment under INA 204(j)
Answer: Yes, as long as the requirements are met. First, the key is whether the employment is in a “same or similar” occupational classification as the job for which the original I-140 petition was filed. Second, it may be appropriate to confirm that the new employer and the job offer are legitimate through an RFE to the adjustment applicant for relevant information about these issues. Third, as with any portability case, USCIS will focus on whether the I-140 petition represented the truly intended employment at the time of the filing of both the I-140 and the I-485. This means that, as of the time of the filing of the I-140 and at the time of filing the I-485 if not filed concurrently, the I-140 petitioner must have had the intent to employ the beneficiary, and the alien must have intended to undertake the employment, upon adjustment. Adjudicators should not presume absence of such intent and may take the I-140 and supporting documents themselves as prima facie evidence of such intent, but in appropriate cases additional evidence or investigation may be appropriate.