Learning WordPress from the Ground Up.

Hi all
I am trying to learn how to develop themes with as much functionality as possible. In other words, I want to become a WordPress expert.

In my quest, I have been taking tutorials and reading the Codex, while trying to develop practice themes. But I realize that there are gaps in my knowledge. There is a progression to any learning experience. I understand all basic functions on the WordPress panels. I have a working knowledge of HTML and CSS (I still struggle with CSS, but I know where to go for help and can understand what they tell me). I understand basically how PHP is structured, and can often figure out what is going on by reading it, but I cannot write it. I am currently using the Thematic theme and building a child theme.

My issue is that there are gaps in my foundation. I need to someone to point me to “First, understand this concept, next learn this, then go here…” I know at some point I will have to learn more about php. Should I work on that now, or can I wait until later? This whole issue came up because I was trying to understand filters and actions. The Codex confuses me a bit still, but the tutorials out there seem to end right at my level of understanding.

I also posted this in the WordPress forum on Reddit, if anyone would like to follow the answers. Same Title, same screen name.