If you are modeling a healthy balance in front of your son, then great! It does not matter how enthusiastic or stoic you are. Most importantly, do you. That goes a long way with kids. They can see when you are not yourself, as you have stated. You two have different styles of relating to your son and that is OK. You are individuals in a family relating together.

My partner is a pretty reserved guy, most of the time. I have accused him of being emotionless. But he is not. He just doesn't express them as enthusiastically as I do. Our boys appreciate this difference between us, because they know who to go to if they want a big cheering section or just a little pat on the back.

Enjoy the differences.

ps- I can understand the switching between "our" and "his" son. You, as you stated, are new to this parenting thing and so is your way of expression. As you grow into it everything will change.