Big wordpress website with extended user governability

I am in the process of choosing a WordPress template which I will inject with a design of my own devising, which can then be reiterated by the user publishers.
The template should have some fairly intelligible publishing features (for the 2000+ user contributors) which lead me to consider the following features as necessary:

• Agile in terms of design implementation
• Strong user governance (tailored user access at variable levels to custom made elements, widgets, templates etc.)
• Accessibility-considerate coding
• Documentation and 24-hour support
• Responsiveness and generally adhering to current web standards

The price is a non-issue as long as the template is entirely stable and can provide the listed necessities.

I’m immediately thinking Divi, but I’m hesitant when it comes to the issue of user governance, as the users will not actually be building any elements themselves, but simply rehashing my own designed elements.
If anyone has prior experience or advice on this topic, it would be greatly appreciated!