Indeed, the Casali brothers immediately spring to mind. They started making maps for Doom before they were snapped up by iD and commissioned to create Final Doom. They were probably a special case however..
As for a Phd, well I was in the same boat as you when I was in 5th year – loads of ideas and thinking far ahead. As time went on however I decided to, well lets just say live more in the moment…you have plenty of time to be worrying about Phds once your in college. Your main priority should be deciding what course to apply for and in the meantime the specifics of this project of yours. Kyotokid is right, get yourself a cheapish engine such as Torque and see how you find using that, then you can make your way from there.
Remember though that developing a game its not just programming skills your going to need, theres also the textures and other art work you need to think about. Now one of you may want to concentrate on this are or as has been mentioned you could “rope” someone else into it who may have the required skills. If you take a look at the Programming and Creative Content forums of this site you’ll see other nice tidbits of advice for small projects. Trust me they’ll come in useful as I’m seeing for my own project so far… :D