It's nice hearing you planning and dreaming about games
. And it's good too, it will make you persevere till the moment you'll deploy your actual game. But given you need to learn everything from scratch, maybe you should start by reading some tutorials and asking questions around here
Basically if you're thinking about 3D in java, make sure to have a good understanding of scenegraphs and what currently is available/working. Then start experimenting with one(by following tutorials or online books). Whatever libraries, and technologies you might encounter and try to learn, as a beginner your choice should heavily rely on available documentation and learning support. You might also consider starting off with a simple 2d game. A 2d game will help you understand at first hand the very basic principles of writing any game.