Yes - it can be civil.
And I’d caution against being very aggressive in wording of solicitors letters (that doesn’t mean not being firm). When the anger does hit, you will want to lash out, but try to not bring emotion into it. I’d keep all correspondence polite and respectful. Maybe write a response and give yourself 24 hours before reading again and responding. Be angry, but don’t let him see your anger- it only raises the temperature, and will make him defensive.
don’t use your solicitor as a therapist- it’s expensive and they aren’t very good at it! Start going to therapy/counselling right now.
the grey rock approach is good. Keep communication to texts and emails, so there’s not misunderstandings and you have time to count to ten before responding. Keep them all polite and with neutral language.
also be prepared for him being angry and lashing out. ( even though, or perhaps because he caused it.) Try not to respond immediately to nasty or aggressive emails and messages, or stoop to his level. And try to forgive him a bit for that.
Don’t get too hung up on things that don’t matter in the long term- the case and painting are good examples. People end up spending £££s fighting over granny’s teapot and the bitterness and resentment lasts for years. Take the high road where possible.
mediation can help, and a good mediator will set a respectful tone, so it’s a good place to have face to face, calm discussions. But it’s always a good idea to talk to a solicitor first to make sure you know what you’re entitled to as a starting point for negotiations.
finally, I’d also caution against settling for less than what is yours. The agreement has to be sustainable. Don’t let him persuade you to let him keep his pension- you have taken time out of the workplace and even if you go back, it’ll be less. Same with bonuses- these are family income. Don’t find yourself at 65 feeling angry that he has a comfortable retirement while you have to settle for a lower standard of living.
he is not your friend right now, so don’t shaft yourself in the hope that he will like you. It won’t make a difference. Being friends again is something that might come after the divorce, but right now you have to make sure you get your fair share of the family wealth. ( which you’ve both worked equally for- he couldn’t have had his career without you taking a step back).