You can view the tutorial for the press stack here:
You will find the ability to change the width of the button under the "Button - Initial State" section, and this option is titled "Fill Mode". Here you can choose to set the fill mode to Auto (fits to inner content), Fill (fill the container), Pixel (Sets a specific pixel width), or Percent (fills a percentage of the container).
As for multiple lines, it appears that you may have some padding around the "Button Text" portion of the stack, which is why the longer lines are not extending towards the end. If you remove the padding, the text should stretch to fill the space.
By default there is not padding on the text, and the button fill mode should already be set to auto.
Lastly, there isn't currently the ability to inherit from the page font face. This will need to be added in a future update. Although, for the time being, there is ability to set a custom font, which you could easily use to type in the name of your current pages font-family.
I hope this answers your questions. Thank you so much!