I don't see any reason not to use QML and C++. Since you're targeting the N9, the only other sensible option would be to use QML and Python. I would suggest C++ because not all MeeGo-Harmattan APIs have Python bindings, and the usual benefits of Python are lessened when using QML for the UI code.

You should define any large components (Page, Sheet etc) in separate files. This is neater and also allows reuse of the components. QML does not have the OOP features that you are used to in Java, but you can make use of inheritance by basing one component on another. You can also define your own properties for a component. Properties can be of type string, int, variant etc or they can also be a QML component. C++ objects can also be exposed to QML.

My advice would be to take a look at the documentation both for QML and Qt Components.