Better start with something small, you'll never finish a 3D racing multiplayer game without any experience in creating games.
2) I'd say learn D3D IM or OpenGL and write an engine. Work on it until it's quite good. You can use it later too, but it's not such a big project, so that you can finish it within a few months. Then start working on some bigger projects, but finish them all.
3) Visit www.perplexed.com/GPMega/ and read the interview with Andre Lamothe.
4) If you wanna create some sort of multiplayer racing game, do it 2D at first, create a working network system. Later you can easily convert to 3D.