How to correctly distribute tables across django applications?

Question

Django

I study Django in combat mode for myself, I write crm. In order to immediately choose the right directions, the following questions arose (I ask questions separately so as not to confuse the discussion.
3. How best to make the structure of the application, for example, mail is a separate application, orders are separate, but directories are also needed that will be used in different applications, such as materials, products, units of measurement and so on, is it better to make a separate application under the control of directories? and how to connect them with applications at the base level or somehow differently?
Yes, I read that applications should be independent, so I have nothing to do with the design of the structure .. .
Will there also be various settings, for example, for the mail application, will it be better to manage and store them in the application or make a separate application where other applications will be configured?