First of all get rid of all size fixing. From what I understand your widget looks like the form in the attachment (apart from the fonts of course), is that correct?
Now you have to decide which widgets should change their size when you resize the dialog and where there should be additional space when the widget is resized.Take the widget from attachment and add spacers everywhere you want additional space to be located when you resize the widget and change size policies of widgets you wish to expand to minimumExpanding. Then preview the form and see if that's what you want to get. If not, correct and try again.
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