In my experience, having a teacher is the best way to go. You can watch videos on YouTube, but if you have any questions or need elaboration you can't ask the video because it won't respond. The ability to interact with a person is important because they can give a sense of musicality, how to express through your music, etc. in ways that a video can't. Teachers can also hold you accountable to consistent practicing, which is I find helpful. For a while, I did what you're doing, and it seemed to work out pretty well for me... except there were always a few trouble spots in certain songs that I could not figure out on my own. As you move up in skill, the music will get increasingly complicated and it eventually gets to a point where you will need a teacher. It is a good sign that you have the initiative to practice on your own and move forward with or without a teacher/resources, etc. I find it refreshing, and I do recommend a teacher if you find the music becomes more frustrating than it is enjoyable. I'm not too familiar with book series except Suzuki and Alfreds... both of which I dislike for personal reasons (though they can be useful resources). Just know that not all series are the same and they apply different learning theories that may or may not work best for you. I'm curious as to what others have to offer on these various topics.