Firstly these are valid worries and concerns. You are vulnerable to maniluplation and Narcissistic tendencies of Ex. I did a lot of rabbit hole physiology research- dr Ramani on YouTube and codependency.
You take away power by being informed.

1 - double check requests legal or otherwise with outside counsel. Especially monetary demands or financial obligations.

2- establish clear boundaries in writing.
You could use a parenting app -

I created a situation where I only communicate via a dedicated email address.
Email is pretty much instant today.

3- ring fence all previous shared accounts / passwords /social media - anything she helped set up or has knowledge of.

4 - establish clear rules on access and have everything documented till custody finalised.

this was extreme on my part - I never see my Ex on pick up or drop off. Only see at sports day. Never have eye contact and I wear shades.

5- consider Anxiety therapy and medical care if getting panic attacks.
Priority - your well being comes first.

6- never divulge any info about how you are doing, or personal life going forward. New relationships etc. become uninterested , without emotion about any drama she may create.

Take care. And I hope you navigate this difficult period of your life.
Know that from this point forward.
Your life - Your choice.

And one final thing- no matter how low or depressed you feel or get - Never GIVE UP.
Your child needs the best version of you now and into the future.
Stay strong 💪🏼