Designing a good Admin module for website user management

I have just finished building a website - kind of. I am doing both front-end(css, html5 etc.) and back-end(Golang echo & pongo2). So the act of programming is not really an issue at this time.

I do however need a custom admin section.This admin section needs to be more complex as the company grows. Also, it needs to be a custom built solution as Golang is still new. My problem is that i have searched the internet for the correct design or design flow of admin logic but all questions seems to be related to coding it.

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What is wrong or right with this design logic?

• starting as a user with root level access.
• create a json file or any file with predefined superadmin users.
• create an admin login page.
• superadmin user can log in here to only create an admin user administratively.
• admin users can login here and perform their functions.

Is this how this admin thing is usually done?