If a Google Apps Script Web App is being run by another user, does it consume the user's quota or the owner's quota?

I am new to Google Apps Script and programming in general. I am actively reading Stack Overflow questions and official documentation as well. For question number 2 below, I couldn't find any information, at least one which I could understand.

I have read about App Scripts Quota and have few doubts regarding that. My apologies if it is a duplicate question.

Question/Doubts:

Let's say I have a script and I deploy it as a web app, while setting Execute the App as to User accessing the web app.

1. Now that while I ran the script myself it was consuming my Quota, whose Quota will it consume when another user runs the app as himself/herself?
   
   Reading this and this question on Stack Overflow I think it's his/her quota that will be used.
   Am I correct?

2. If my script is using Advance Google Services Standard GCP Project, I manually enable APIs in developer console.
   
   What happens when an user runs my script (deployed as web app) and he/she didn't enable API?

Edit: Question 3 removed as it deviates from the topic.

I hope my questions aren't too broad instead of being specific and adhere to Stack Overflow rules. I will really appreciate any information that clears my doubt.