Install ERPNext along side other websites

I have been trying to set up app ERPNext in a VPS (Ubuntu 20.04). I have followed different step by step guides and managed to install a working production environment for ERPNext. But I have different requirements.

I plan to host a few domains on the same VPS server (my concern is not space or server capacity).
So, I need to set up wordpress in and erpnext in erp1, erp2, erp3 subdomains.
I need erpnext in
I need normal php websites in 3rd domain.

I am comfortable with running commands in Ubuntu 20.04.

My questions:

  1. How can I achieve the desired result ?
  2. Do I need to create different databases and different mysql user for different erpnext instances in same domain and also on different domain ?
  3. Is it possible to install bench in directory other than /home/user/frappe-bench; for example inside /var/www/site1/html ?
  4. What is the difference of creating a new erpnext production instance by bench new-site and creating a complete different branch for production ?

I am looking for some detailed instructions to answer all my questions.