I have some user controls in a windows form. I wonder
if i set the Font property of the main form, will its child get a) a copy of the new
Both. The Font property is its own .NET object. Winforms however caches the native Windows font, they are fairly expensive to create. The .NET wrapper object is quite small.
Yes. The code is fine, the Font property setter already disposes the previously assigned font.
Yes, it is disposed by the UserControl. Which in turn is automatically disposed by its parent.