It is an interesting educational project but staying away from Unreal or Unity3D is really a tough decision if your project is going to need some more features that are already developed and well tested in one of these engines.
In my experience, the real value of the engines aren't "features", but tools oriented at level designers and artists. Once you have a project with 10 or more members, managing art and assets becomes a real headache - and most of homegrown solutions, as well as open source engines start to fall apart at this point.
