How to customize "New article" page

I need to customize the "New Article" page in the Admin area. For instance, I don't want my users to have access to the "Extended article" button. Also, I want to make the "Start date" and "End date" fields mandatory.

Ca this be done through Preferences or do I need to rework the code behind this page? If the answer is to rework the code, what file do I need to change/

Thanks in advance.

Don