One thing that really has helped me with e.g. writing an email that I dread writing is to just write a draft that I don't plan to do anything else with than use as a starting point when I write the real email that I won't write until tomorrow. Often the draft is good enough to send after only small edits. Or the writing of the draft have helped me to clarify my thoughts enough, combined with a night of processing, that writing the real mail the next day becomes relativly easy.
My trick to start emails is to add To and Cc last, when I'm happy with the email.
If I add them first, I worry that I'll click send by mistake halfway through my draft (and a secondary worry is that the draft will be full of inappropriate stuff and curse words, which I never add even to drafts, so it's not a rational thought). If I add the recipients first, it also feels like they sit there looking at me expectantly as I write, which makes it harder.
An email not addressed to anyone, but of course with the recipients in mind to adapt the content, makes it easier for me to treat the first version as a draft.
Sleeping on non-urgent emails sounds like an excellent idea, because your view of the issue may change.
This is a good strategy for contentious topics. That said, I would argue that the best thing in this situation to get the task done is to call the person. That way you can hear them, react to them, and the task is done at the end of the call. That said, I don’t know anything about your email, audience, etc so you do what works for you.
My underlying hypothesis is that too many people are afraid of making phone / video calls, but it’s a much better way of getting difficult things done sometimes.