Your question is not a simple one to answer, mostly because you are asking a lot of complicated small questions wrapped up in one big question. I am going to focus on one sentence:
So, generally or specifically: how did you grow your knowledge and get to the point where you were able to create your own game?
Practice. Start by making a simple pong game. Then add some features to it, such as a menu screen and game options. Then make something more complicated, like a Bejeweled or Tetris clone. Then try to make a small adventure game. When you think you are getting good at making games, post a download link on a game developers forum and have some people play your games...if you survive the harsh criticism, use that pain to make your games better.
Only after you make several small games from start to finish will you understand how to make a big game. Seriously, this is the best way to learn
. School can help, books can too. But hours spent at the computer making your own games, and examining other people's code, will be where you get your greatest knowledge from.
There is a larger question in there that you are asking, and that is "how do I break into the gaming industry?" My answer is still the same: practice making games, all kinds of games, until you understand the process. When you finally make a game that is worth selling, just contact a few distributors and let them see what you've made. Send review copies to gaming magazines and websites. A good game will generally sell itself.