It was not very clear to me on whether or not one is able to access whole classes across modules. I know functions can be imported, but can we say the same for classes? Is it just a matter of importing their constructors?

You cannot import a constructor, but you can import a function that would create a class and return a handle to that class through an interface that both modules understand.

The other module will only be able to work with the class through the interface though. Trying to cast the handle to the class type will return a null handle even if the same class has been implemented in both modules.