I don''t see any conflict generally in filing an EB-2 NIW while an EB-5 is pending. Specific factors may affect one or the other, of course. You should probably seek advice of your immigration attorney for a formal opinion.
There is no prohibition against filing an I-140 when you have a pending I-485 based on approved I-526 petition. Possible negative effects on the pending EB-5 I-485 could arise if there were inconsistencies in the information included in the I-140 and I-526/I-485 filings, e.g. about your employment history or other material matters.
You can file simultaneously file any immigrant petition under different preference categories, and the petition that is approved by the USCIS and whose priority date comes current first is the one you can use to immigrate through. With this in mind, your investigation of an EB-2 National Interest waiver is a good choice, so long as your supporting evidence is both ample and impactful. National interest is more than just positivity. It is something that affects this country greatly. We are able and ready to assist you in this effort.