I'd advise you to take a top-down approach to create the game.
Going into details at first, like the fonts and sounds, is only going to complicate the implementation. Put some straight requirements, do a draft, a simple storyline, some use cases (as in gameplay and how the player actually plays this game),some mockups of what the games will look like.
Once you have those stick to them and creating the game will only be about putting the ideas into code.