AddressBook Turtorial vs Designer

I am still new to qt and try to do the address book tutorial with QT Creator.

The tutorial does the manual approach and I ask myself if some properties of widgets are manually set which I cannot set in the designer?

E.g. I just learned the hide()/show() and setEnable() is not the same. The latter one can be set in Designer but the 1st ones are referred in the tutorial. So how do I hide the 2 buttons initially in the designer or set a lineEdit to readOnly?

Same issue I have with the 3 buttons spread across the grid cell. I am not sure how I do a QVBoxLayout->addStretch(); in the designer.

Another question is about slots. I added slots manually in .h and .cpp. But they didn't show up in the designer, when I tried to connect the buttons to them. I had them to add manually to the list of available slots of my main widget.

I would have expected that they appear or that they are created if I add them to the list and they didn't exist before.