Absolutely. Normally, there are nerves that run along the ribs providing innervation to the chest. After a sternotomy, those nerves get occasionally damaged and this is where your numbness likely comes from. Because you are able to exercise without any limitations or symptoms, the likelihood that this is in any way related to heart disease is extremely low.
Yes, You will be absolutely normal. But, before that I will advice you to read one book. It will help you to know more on it. "The Patient's Guide to Heart Valve Surgery by - Adam Pick."