Sounds like your ex has really knocked your confidence. You know the answer really but your ex pushes your boundaries and makes it seem like you are unreasonable.
I say this knowing my ex made me feel the same way.
My top tips... might not be 100% correct but they have worked for me.
-Gp- get referred to counselling and work through this to build your confidence.
-block all forms of contact except one email address. I know you are worried about your older kids, however a happy mum is better for them too and you need that space
-set up an email address just for your ex. Check when you want to.
-don't encourage your eldest to respond to texts. If they don't, whatever their reason is, let them move at their own pace and reasoning. Don't encourage out of guilt. Your kid is old enough to have a phone, for dad to contact them, and for them to make a choice on how to respond.
-daily updates is a definite no. I would outline your suggestions for contact every other weekend and a weekly update in-between with a video call. Set dates and times, so Thursday at 6pm is the phonecall, or whatever works for your schedule.
-half terms- tell him the plan, maybe suggest the same days each school holidays or split the half terms. Whatever you think is reasonable. Or you'll end up waiting around for him to let you, and he will leave it until the last minute so can't enjoy or organise your own life.
-baby seeing dad a couple of hours at a time is reasonable, they are young and needing you, especially if you are choosing to breastfeed.
Now by the way you have written your post, setting these boundaries will likely result in your ex making threats, such as court. So you may want to consider creating a little plan and seeing a solicitor to go through it and see if it is reasonable. My solicitor telling me I was reasonable made me feel more confident in standing firm. And it has put me in good standing in court since.
Unfortunately your ex appears used to making all the decisions, and you doing what he wants. In order to heal, move on, and set up your new life you will need to put boundaries in place. When he breaks those boundaries again, because he has already, you need to hold firm and not give in. Wishing you well as I know it is so tough.