I’d love to work with the community to build it. The project is beyond a 1-man scope. The goal is to make the Sword Art Online Seed System and create a development SDK that’s easy to use so anyone can make their dream game.
Dunno about game engines, but I’d check out godot. It’s a open source C++ game engine you could maybe poke through it’s documentation and source code to understand how it does structuring
Side tangent, if you’re looking to create your own game engine, this guy talked about his c++ game engine development process