Those all sound like things that Discourse has already.
The easiest way to do that is to just host them somewhere else and add links to them with a theme component and have that site themed to look the same as your Discourse site. People don’t notice URLs, so if you keep the navigation on the other sites such that people can get back to Discourse, then it Just Works and nothing fancy is required.
I"m not quite sure what that means, but if you really want to add whatever your custom features are to Discourse then you’ll need to create them as plugins or theme compononents.
It’s not clear what your aim is.