Hello,
I am an Linux expert with strong expertise on OpenWRT. I have done similar projects. Please see:
https://www.freelancer.com/projects/Linux-Embedded-Software/Customized-OpenWRT-Busybox-Build-Code.html
https://www.freelancer.com/projects/C-Programming-System-Admin/bonding-router-firmware.html
Regards,
Iosif