How do I create a custom template of channels and categories

Here is my use case:

mattermost installed at xyz…com

initial signup for admin using /signp_email (works as expected)

Instead of requiring new users to be invited I want new users to be prompterd with ‘create account’ when going to xyz…com

When new users sign up I want them to be required to create a team (their own name for example) and then have their team pupulated with a standard teamplate containing categories and channels. Every person will use the same template to start with and can customize it after their intial login (or leave the settings as is).

Has anyone done this type of customization and if so, what files did you modify (I am a novice developer with not much react experience)