I don´t feel like using something like Box2D, I much rather wanna do as much as possible myself.
Be careful with that. It might seem exciting working on everything yourself; however, you can very easily be overwhelmed trying to deal with so much at once. And this can be a major factor in losing the desire to work on the project. These 3rd party tools can be a real lifesaver, as they can take the place of a section of code that you may not want to work on, or may not be ready to work on. Now, this isn't to say that you should go and use external libraries for absolutely everything; but, you can put a library in-place of the systems you don't have the time, experience or desire to work on right now.