If you ever find yourself in this position, or if you are the author, please, please, please, knock a bunch of rules together using tools no more technical than pens, paper, whiteboard etc. and play test it to ruddy heck before you so much as create a software project.
Even if I think there's a low probability that the project will be completed as you describe, don't be discouraged. Any progress made in any direction will be valuable experience, and enjoyable. I have started more than one project that I couldn't finish and I've never regretted any of them in hindsight.
Don't be afraid to fail publicly, by which I mean post about absolutely everything you've done, no matter how unfinished it is, it'll help everyone keep enthusiastic and engaged. If you complete the project, you'll have a valuable log, if not you'll be able to see both 1) what went wrong and 2) the sub-victories you had on the way.
Good luck.