I'm building a web platform to allow users rate/review a niche group of organizations and consultants.
If you'll be blogging about it, you should make your identity known. You may decide not to disclose the details of the project, but you should always be transparent regarding what you're trying to do.
Hiding one's identity or not describing your real motivation can "kill you" online pretty quickly.
Regarding the legal implications and best practices, maybe you could take a look at some similar sites like www.Yelp.com, a website where people post their reviews (good and bad) about products and services. They probably have some sort of rules&policies about how it works.
Hope this helps