I am planning on creating a massive multiplayer world and I am wondering where to start. I am quite inexperienced in the field of Java but I have researched into it and learned that it is perhaps my best bet in creating this project is Java for the fact that it has a much easier learning curve than C++ to beginners and still capable of holding massive amounts of players at a time. My question is simple:

Should I start the game by creating a single player prototype and introducing multiplayer later as I become more experienced or start with multiplayer before I am completely experienced in the field.

Thanks for your help!