From what I’m aware Proximity Prompts only hover over the part you put them in and don’t act as a ScreenGui. You should probably instead just create a separate interface in StarterGui and enable it whenever the client gets within a certain distance of your selected part.
I recommend using remote events to activate the GUI as it’s a better practice but you can also use RunService in a LocalScript. You can get the Mangitude between the players position and the parts position and if its less than or equal to the activation distance than you can toggle your interface.
Yes and no. By default, you can’t. You would have to get the proximity prompt GUI and manipulate it yourself. A way to get the GUI is to make a proximity prompt, get the proximity prompt to appear, go to PlayerGui and copy the prompt.