Pawan, long time no talk! =)
Let me see if I can get some of your questions answered fairly quickly.
- Unfortunately, there are no app contributions available in the Admin Console, the best we have are extension points on the "Settings" screens reserved for Place Admins.
- Currently, there is not a check for System Admins ... but this is something that is being discussed for the future roadmap.
- Yes, per comments in 1, if you use the app contribution Place Configuration, this naturally aligns with that permission scope:
Keep an eye out for upcoming webinar announcements and training curriculum around these topics.
BTW, I meant to post this yesterday, but I added my admin-essentials add-on code to GitHub yesterday so you could see it in action. Simply grab the code and throw it into your own add-on, and you should be good. If you add any features/do any improvements, would appreciate a pull request to share with everyone =)