Well done for getting out.
I have no experience of this at present but I'm sure its coming. Firstly, keep all email and abusive correspondence (you might need them later).
Disengage, disengage, disengage. He's a twat and uses contact with his children to continue his abuse of you. You can not reason with people like this, you are not responsible for his actions.
Arrange a fixed contact schedule; by accommodating his schedule changes and whims you give him the "in" to continue the abuse, if he refuses, consult a solicitor (hopefully this will not go to court).
MissPricklePants suggestion about the exchange of important info statement is a good one, keep it simple, don't let him use it as an "in" to engage further.
Any accusations he makes about you being inflexible, mean, selfish, blah, blah, blah are said to make you second guess yourself and for you to relent, be strong, theses are just more tactics to first engage your attention, and then to abuse and control you.
In the future when he learns to behave you can try being flexible but right now he needs to learn that being a dickhead is counter-productive, so ignore twatish behaviour. My ex used to, and still does to a certain extent, use my sense of fairness and my love for my child as stick to beat me with.
Good luck