Hello AndreElijah,
You bring up some great points and questions. The best way to provide you with the most in depth answer, and an overall idea of how to develop for mobile would be to direct you to the documentation page. The pages provided below contain the answers to all of the questions you have asked as well as guidelines and important optimization points.
Mobile Development
There are sections within this documentation to separate key topics to better highlight certain restrictions and features when developing for mobile.
The answer to your first question is simply, yes.
Mobile ES3.1
Feature Level Switch
These images were pulled directly from the documentation pages. Here are a couple of quick links for these pages.
Performance Guidelines
Materials for Mobile
Let me know if you need more information or have further questions!
Cheers,