Neutering is a very good idea if you aren't going to show him in conformation. It has many health benefits and it won't change your dog's temperment at all! I hear people saying the earlier the better but the more and more I research I see that large dogs should be altered around 18-24 months because this is when they finish growing. If you are going to wait that long make sure he is with you at all times, you don't need any children from him!

Prong collars are wonderful if they are used correctly. Not sure what you are doing when he bites but you should be doing a quick jerk on the leash and say "NO" in a firm voice.