Would the eurofox be in the right weight category to count for hour building towards a CPL? Not sure under new EASA rules what goes for hour building towards CPL, just know that microlights don't count, you'd have to check up on the status of the eurofox.
You say you want to buy it, operate it so he can build his hours then sell it to fund the remainder of the training. You won't be making any money on it, so why not just spend the money on training at a proper school like everyone else does, rather than investing all your capital into an aircraft where it will be tied up if you are unable to sell it at the end. Aircraft ownership is very expensive, and an aircraft sitting in the hangar isn't doing anyone any favours. The best rate will be at a busy FTO where the aircraft are flown almost as much as possible, and if it breaks down for any reason there will be another one parked right next to it also owned by the FTO which you can take on. What happens when you get a prop strike or someone cooks the cylinders while tugging? who's paying for the new engine?