Not that easy since we have no idea what you actually are doing!? Or what your plan is since you change it from time to time?
Have you ever installed and used a working OpenWRT so you have some basic experience?
I don’t really get why you ask some of these questions if you have basic experience with OpenWRT?
Most users start with the pre compiled versions a couple of years. Some after that move on and start making more advanced configs and so on.
But not many start by building from source code and then ask how to make basic configs?
Are you still trying to build a mega much custom image from scratch without OpenWRT experience?
Have you any working LuCi GUI?
What is your backup plan B if you succeed and compile this image you are working on and you after you installed it can’t connect to the router?
It is a lot less headache involved to install a standard image (or a imagebuilder image with some favorite packages and/or absolute basic minimum config setup) and then from a working router run a setup script that do all settings in a couple of seconds. If something fails then do a reset and start over.
And the prize for building with source code is that you should be able to read the user guide we have on the homepage.