So you separated without something formal, but wish in retrospect that you had something formal?
What factors do you think allowed you and your XW to stick to your informal agreement? Did you end up going through mediation?
My W and I have committed to going to MC (probably should call this "couples" or "co-parenting" counseling at this point). I think this is a critical piece to maintaining trust in each other. I know things may change along the way.
Financial - my W told me the other night that if we D she would rather have ME split up our assets than the lawyers. That she trusts how I have managed our money in the past. Obviously, this is informal. I thought she was nuts. Even I wouldn't trust myself to do it correctly.
Custody - written or not, if we trial separate and let's say we have a 50/50 custody arrangement (informally), that plays when it comes to the law. As long as that's what we're doing during the trial separation I am not really concerned.
The bigger piece in support is spousal support in my state. As much as I don't care about money right now, and it sounds cold, it will only benefit me to assist my W in getting back to work during the separation.
