Kap: everyone here has good and experienced advice for you, but mostly, you already have it for yourself. Read back over your writing. Step out of your emotional response to him for a moment and see what you are already telling yourself. Follow your instincts. Bottom line, if you don't care, he can't hurt you. Sure, you can admit you're still scared of him, that your relationship still has a charge on it, but you don't need to let him in on it.
I must deal with my ex N on a regular basis, as we have minor children together. He uses absolutely everything I say or do and twists it to his advantage. I have learned to only respond to the content of his emails when it is absolutely necessary. I, too, wish I could respond with reason, with "don't you see what you are doing?", but those responses are for a reasonable person, who could actually grasp your response, or who truly cares. He can't.
When my ex spews his venom/attempts to manipulate in his emails, my response is very simple: "recieved your email. thanks". If it is a phone call and he starts that, I will hang up. He rarely bothers to call back. If I don't engage in his fights, he has only himself to blindly swing at. Once again, if I don't care, he can't hurt me.
(yeah, drives him nuts, but so what?)
Yup, leave him to twist in the wind. He is not your problem anymore. As far as your kids go: mine are teenagers and I still have to let them come to their own conclusions about their dad. Except for doing what I can to positively influence their life, he is their dad, and they will learn what they need from him (good or bad). Your kids are older, rejoice that you can let that go and focus on your own wonderful relationships with them.
You are fine. Don't engage. You don't need it (love the response about a good car mechanic, etc!!)