OpenWRT Setup on Linksys Router

I need assistance setting up OpenWRT on my Linksys WRT1900ACS router. Currently, it's connected to another modem in bridge mode, and I can't find the default gateway IP.

Requirements:
- Set up OpenWRT and secure it with custom firmware security.
- Configure a PPPoE script function for my PS4 to run an exploit from a port on the router.
- Remotely access my PC, set it up using SSH access, and provide a brief guide on what you did.
- Allow me to set my own password.

Ideal Skills & Experience:
- Familiarity with OpenWRT and Linksys routers
- Strong understanding of IP addresses and router configurations
- Experience with SSH and secure access setup
- Ability to provide clear, concise documentation

You can bid over $30, but what you bid is what I will pay. I don't want to discuss the price, and I will simply block you. Thank you for understanding.
Ensure custom firmware security with strong admin password settings and firewall configurations.
Write a script to handle port forwarding and set up new WiFi with secure or no security options.
Make it easy for me to use the script for port forwarding and allow access from outside my home.