If you want to change the position of the elements but not just vertically, use a Grid instead of a Stack . Because with Stack you can not align 2 elements to be side by side. Grid, on the other hand, allows you to arrange the elements inside the grid however you want and you have complete freedom to make changes in different breakpoints.
Regarding equal spacings:
At first when I set margins and padding I only use pixels - only after everything sits the way I want do I convert the pixels to percentages. In addition, I make sure to do the conversion from pixels to percentages when the width of the canvas in the editor is as wide as the width of my computer screen, to see the design on Live-site as I see it in the editor.
For example: If the screen width of my computer is 1680px I make sure the width of the canvas is also 1680px.