Everyone is giving great advice. You can see there are many possibilities with your project.  Your project also can depend on some other factors such as Local codes (Arg!), how much power you realistically wish to generate, how much money you want to invest in it, the possible noise any 'gearing' might make to nearby neihbors, and how pleasing to the eyes it will look in the end.

It looks like a very fun and beautiful 'artistic' first project for you and your cousin.  I personally love the looks of those water pump mills. I think most people do. It is very 'non-threatening' to the eyes.

Currently, I also am making something very similar to what you have, for generating, hopefully, 'pretty good' electricity.
Mine will be a SIMULATED water pump mill, but it has only 8-10 thin carved blades at a steep angle (4 degree blades) for much more speed than the high torque slow metal blades on your metal mill.

The blade rotor on mine is going to be about 6 feet diameter and directly hooked to a low rpm 'normal' dual rotor alternator (made W/small trailer hub)  such as made here on this site countless times. It will be about the same height as yours.

The simulated "water pump mill" I am putting up will look more like just a big 'yard decoration' with flower planters around it.  

Have fun with your project, keep asking questions, and always be safe.