Definitely keep any discussions on email - much easier to print out and preserved, and much more professional-looking if you have to wave them at a court, if he decides to be a prat about residence/contact. Judges don't tend to be terribly keen on scrolling through text messages 
I'd be inclined to send a single detailed email setting out your position, and then refuse to engage with anything except contact/financial arrangements. Just keep repeating 'We need to discuss DD. I have explained my position and the relationship is now over.
I would suggest something like:
'I wish to address the points you've raised as you appear to feel that you have, in some way, been badly treated. Our relationship is over, but you will still be in DD's life, and it is in her best interests for us to have a functional and courteous co-parenting relationship. This will be difficult if I am constantly having to deal with accusations of unfairness towards you.
The break down of the relationship was accelerated (although not entirely caused) by your refusal to accept my decision not to allow you to take over my role in the business which I have built up, entirely on my own, and which is now successful. I was not recruiting and there was no role for you in the business, unless you intended to take my place at the head of it, and render me effectively unemployed, and it would have been entirely unprofessional and inappropriate for me to effectively create a non-existent role for you, simply because we were in a relationship.
I was extremely hurt by your refusal to accept my decision, despite it being explained to you on several occasions. You continued to push the matter, and to use DD as a weapon against me, by stating that me continuing to work in the business was detrimental to her well-being. I am proud of what I have achieved with the business, and I am proud of being a good mother,and good role model, to DD, and this accusation was central to me deciding that I could not continue in this relationship.
I have repeatedly asked you to spend more time with DD, and you have declined. I have asked you to contribute financially, and you have declined, stating that I didn't need the money and querying why I felt you should support DD financially.
Our relationship is now over. I will not reconsider my position. DD is now the most important thing, and I will facilitate her having a relationship with you. This is important to me and I hope it is important to you too. The financial support is an entirely separate matter to the contact.
At this time, your working arrangements are [insert details] and DD's arrangements are [insert details]. I would therefore propose [contact] Please let me have your thoughts on this proposal.
In terms of the financial side of things. If your income is [income] then the CSA's estimate of appropriate child support is [estimate] I am aware that your financial situation is [insert details]. I would therefore propose that you pay [calculate reasonable amount that can't be suggested to be unreasonable]
I look forward to hearing from you and hope this can be resolved amicably.'