Fresh air is fine as long as it's not too cold or hot. Avoid crowded places where someone might get in his face and sneeze on him. 70 and sunny sounds great, even if you just sit out in the backyard with him.
Bank drive through would be better than taking him inside. Piano lessons probably fine, unless there would be other kids around that would get in his face. I would worry more about germs from other people than anything else.
BTW, congrats!!