How to decide whether to make a separate class for widgets of a window?

[Lykurg]

E.g. you have custom widgets A, B, C, and D which should have connections. Then make a QWidget W and in its constructor initiate ABCD, arrange them using e.g. QGridLayout and connect the signals and slots between ABCD.

This way you only have to initiate W whenever you need ABCD inside your application.