D.L.
In my personal opinion, it sounds like your son is developing above normal. I don't know very many babies with a 10 minute attention span. My nephew was the same way. He is almost four now and speaks phrases in Spanish and knows sign language. Again, in my opinion, let him listen to as much classical music as you can stand. Studies have proven that this promotes learning and increases brain activity. My nephew listened to classical in the womb, he now listens in the car and when he goes to bed at night. Also, Baby Einstein is incredible! I don't know what it is about those shows, but babies are enthralled. They also help to promote brain activity.
What you are doing is plenty. Reading to him is going to promote a love for reading and he'll probably learn his letters faster and read earlier. You can talk about shapes and colors and numbers and he will retain the information. You'll be surprised how much he knows when he gets older!