On the order of 10 non-trivial emails a day. Heavily variable depending on degree of public activity, various cycles relevant to my audience and institutions which matter to them, etc.
"About how much time have you spent on this?"
~Xk hours.
Yes, over ~15 years, very approximately.
"That many?"
Some people golf or watch TV. I have weird hobbies.
"That few?"
It has been occasionally rumored that I am sometimes not on the Internet. I sometimes feel guilty, but that feels suboptimal.