You're best off starting with some java courses, then messing around with the client to understand how it works.... write down every element/aspect that is related to fullscreen (render distance, frame size, sprites/ui component locations etc. etc.) and then tackle things functionality by functionality.
Or hire someone with the funds your server generates.
Edit: Or ofcourse.. rip it from a base that has it (not that I know of any 317 that has it done to an acceptable standard).