As for OpenGL/DirectX, you are probably best off having a look at both of them. DirectX is probably a bit more powerful, especially version 9, so maybe look at that. However, if you get a job with a dev company, you probably won’t be using either, you’ll be using the engine that the company have created using these APIs. Having these skills is what you need to get that far though and the more you know, the easier it is to learn more.