New Restaurant List Guide
Apologies if you are already aware of these, but Eater's Plywood Reports, the NYT's Off the Menu column and NYMag's Grub Street are good sources. As for "(i)nformation that the public would not know," restaurants have to apply for liquor licenses, hire staff, etc., etc., etc. These things are public. There's no way to secretly open a restaurant (and no reason to, that I can think of).