Sorry to hear this and wish you well, it can be a horrible place to be but it gets better, trust me.
don’t agree to anything unless in writing with a witness and get your hands on a parental responsibility form gov.uk and try and be amicable. Go self employed if you can, the csa are unscrupulous. When my kids mom got greedy and went to the csa I realised working 60 hour weeks for less than £100 disposable income per month was no longer worth the stress.