I can see why you'd want to do 'The DaVinci Code', and it does have the makings of a history project but in my honest opinion - don't do it. My teacher told us to always stay away from things involving conspiracy theories, as they never turn out well. It's also a bit cliched...
Another thing - If you find it "really confusing" now, how on earth are you going to deal with it as a major work? This is only the beginning, you don't want anything too overwhelming.
Anyway, I'm sure you'll figure something out
Good luck with it all!