From Halopedia, the Halo wiki
Yes. Sedra City deffo has this.
I went though Nightfall's second stories. And the "Walk the Path" one had a list of Companies in Sedra City at the start. That is either, under "Active Investigation" or "Flagged for Review" by ONI. About 30 Companies are mentioned.
It can be but using the preview function will help you avoid constantly saving "errors" and having to go back to the article to fix it over and over again. I always use preview before saving just to make sure everything looks good before closing out the article.