When we separated, I drew up my own separation agreement since my state doesn't recognize legal separation. We signed it with a notary. Had we divorced, we would have used it as our settlement.
I included stuff like:
1) child support amount and how/when I would recieve it
2) visitation - we went with state std but I put a condition in it that if we both agreed, we could modify
3) custody - legal/physical
4) how we split the joint finances - all the way down to who paid for Netflix
5) who got what car and who was responsible for maintenance
6) health and life insurance coverage
7) 50/50 split for kids' activities such as baseball/soccer
8) allowed attendance of sports/school functions on non-parenting days
9) no overnight visits with him until he had a suitable 2 bedroom place so the boys would have their own space
10) no introduction to new SOs until the divorce was final and we both agreed that the boys were mentally ok to meet a new girlfriend/boyfriend.
We sat beside each other at games because the boys didn't like it when we sat apart. But we didn't talk much. Hi and Bye and stuff about the games. I eventually stopped letting him inside the house. No phone calls unless they were absolute emergencies. Only texts/emails about kids/finances. I even refused to put his name on the gifts I bought for DS13's birthday. Made him buy his own.
IMO, to stay sane, try to remain NC as much as possible. We split during baseball season and I had to see him 4-5 times a week, including the day after he left! It was crazy-making!!
Once I was able to get some distance from him, and we had a routine down, I was able to start building a life without him.
We did eventually R, but we were separated for 10 months, the last 3 of that we were dating again, but maintaining the agreement financially. Visitation eventually became a mute point.
Good luck! It's not an easy task. But there are lots of people here who can help you, just as they helped me.