My self-study plan for electrical engineering
Why push yourself through a degree-style path? So much of what EEs learn in their coursework is of low utility. (I'm a physicist who transitioned to working as an EE. I have never had a single EE course, and yet I find myself with no obvious deficits compared to my colleagues who have.)There are two ways to learn an existing technical-ish subject: you can spend a lot of time reading textbooks, then  do some projects (the "slow-fast" approach); or you can dive in to projects and refer to textbooks when you get stuck (the "start-stop" approach). In the slow-fast approach you will go slowly through a lot of textbooks for a long time, and then in theory you will be able to do projects very quickly once you are done. In the start-stop approach you will start a project, quickly get stuck and spend a while searching for and understanding the answer, then go back to your project.In my opinion electrical engineering, being a subject where fast feedback is generally possible, is very well suited to project-first learning. I would recommend grabbing a few textbooks (Horowitz and Hill's Art of Electronics holding pole position for a practically-oriented learner, in my opinion), reading their introductory material (table of contents, preface, etc.; enough that you know what each book has in it), and then setting all the books aside until you need them. Avoid books targeted at "makers"; most are fine but a sizeable fraction are written by people with no clue what they are doing, and they will actively set you back. (It is very difficult to learn from an author who does not themself understand the subject, and all the worse if they do not realize that they do not understand. Since there are plenty of better sources out there, it's little trouble to just avoid the whole class.)Trying to work on brain-computer interfaces is challenging because it blends biology with electrical engineering. The biology will naturally drive things, because you cannot really control it like you can the electronics. So learning EE in this context is about two things: 1) What can I do with circuits? and 2) What do organisms behave like and respond to electrically? Your project is then using your knowledge of circuits to solve R&D problems relating to bioelectric signals.This isn't easy (I think you know that), but the benefit is that you can quit with "just" EE skills and still come out ahead.