I would advise writing a timeline for ease of understanding for the judge.
Decide what your legal arguments actually are. (Post that here). You are trying to but your arguments forward in way that is easy for the judge to understand.
Print out all your emails/texts to/from ex. Highlight relevant information on emails etc.
I've been dragged through the French courts endlessly for a decade so can't tell you the specifics for the UK but can help with the arguments.
So....
Print out your dossier of emails with your timeline. Probably copy for his lawyer, copy for the judge your copy.
Put the emails in order. Write a historical synopsis of what happened when.
Highlight only your copy. Copy the relevant parts onto a cover sheet for each email so when you read your statement you have supporting evidence without having to trawl back at forth through your emails. Be succinct.
This should build your case. Don't forget to include that ex mil regularly let herself into your house and went through your things. That ex mil is trying to get custody for her. That agreements have been reached then immediately discarded.
So for eg my lawyer was arguing that ex was only interested in attacking me and not actually interested in the DCs. And that he is a professional victim. So she read out all the parts of the emails that supported that.
Then it was ex's turn. He proceeded to attack me, not talk about the children etc and proved her point.
Anyway I hope that helps. Good luck. I'm not sure about witness statements. They're big here but maybe not in the UK.