EVEE: Evee the very epic editor

For a very long time I've wanted to write my own code editor, or even IDE and I've had multiple attempts at this over the years. First there was lua-nano, which was a reimplementation of GNU nano in lua, which I actually ended up getting fairly far into (to the point where you can open edit and save files, with syntax highlighting and even find+replace), but eventually I realized the way I was doing things was deeply impractical. A while later I started a C++ project that was supposed to be more modular called Evee that I never ended up going very far with. A while later I tried to rewrite it in Lua in a project named Leve which got a little farther but again it didn't really get anywhere. But that brings me to evee-rs, my current project which is another attempt at creating evee, this time in Rust and hopefully this time actually something I can get into a little more of a presentable state.

Where to start?

So the first question