We have a widget called "Other page", and is perfect for what you are trying to achieve. You can place the menu
You can place the menu on the main page where the widget is placed not on the page which is nested inside the "other Page". Yes, you can center a
Yes, you can center a textbox in the page which is nested in the other page by using the vertical positioning widget.
Of course, you can simply pin the arrow to the bottom of the page which is nested and it stays there.
You can also have a responsive height for the Other page widget and so have the text box and other content on it acts relatively to the changeable height.