Adjusting Website Viewport for Mobile and PC Users

So I’m normally using common viewport for PC users. As I basically learnt viewport codes for cross-compatibilities (i.e, webkit for Safari and Chrome browsers content rendering). However, I want the website to be accessible for every device and browsers.

Now, the questions are:

  1. Does this require .js file to make the website accessible to every single of device and browsers?
  2. What code would be used to make the task possible? (website accessible to every device and browsers)
  3. How do I make the website landscape-only for Android or iPhone users, thereby forcing users to rotate 90 degrees?
  4. (Optional) I would like to see your recommendation about the cross-compatibility toolkit to check the viewport on different browser and devices without having the website go online.

Thank you!

I only knew basic viewport such as device-width and initial-scale=”1.0″, and I tried to figure out by looking at the Q&A out there (and not sure how I should address the problem on Google).