The structure of a modern professional web service?

Question

PHP

Hello.
We have to write a serious web service project in Yii 2, related to the labor exchange.
I thought about the structure, internal relationships.
There are the following thoughts:
- backend module:
- admin panel - various administrative settings, service management, users, etc.
- REST API - interacts with the database and returns the results in JSON or XML;
- frontend module - makes backend requests to the REST API module and displays the result to the user in HTML (Angular JS, Backbone.js).
In this form, as I think, the application can be easily expanded. If there is an API, it will be easy to transfer the frontend to Android and iOS native applications.
There is a technical specification, but there is no internal structure and there is no API either. I am now thinking about how to make the application initially in such a way that in the future there will be less finger movements.
Please tell me your thoughts, gentlemen, programmers who have experience in writing complex and not very complex web services (serious websites)?

Answer 1

Do you think that all actions in the Admin panel (also related to some internal settings) should be done through requests to the backend API?
I thought that it would be easier and faster to do the Admin panel by linking directly to the database (ActiveRecord). Put in the API only what will really be needed on the side of the site and mobile clients (the choice of a template, etc. is not needed there, in theory).