Atlas dedicated instance hardware requirements/estimates

I am launching a Mobile app using Altas and App Services. I am trying to estimate the initial hardware resources that will be required. I have several questions, based on initial app usage that I estimate in the beginning, daily users will be limited to 100s. I understand that there are many factors that would determine how much hardware is needed and only request estimated/hypothetical responses.

  1. How many daily or active users per time period can the lowest Atlas dedicated hardware support?
  2. Do App Services scale on usage, thus Atlas scale is the limiting factor?
  3. What are the critical metrics to monitor that will indicate I need to begin scaling Atlas after launch?
  4. What resources are there that can help me determine how I need to scale(vertical/horizontal) or what usage metrics will help me determine this?
  5. Do you have any numbers based on example apps or other apps that would help indicate how resource intensive an app is on an Atlas instance?