I have a site in a specific niche that gets great traffic. The site is known as an authority in the specific niches. Many universities and even government agencies link to it. I am going to make a sister site that is a directory for those that support that specific niche. What are the current best practices for SEO regards to directory sites? My biggest fear is that site damaging my authoritative site SEO due to some funky algorithm even though people in the specific niche desperately need some sort of directory to source specific consultants and software.