Maybe him moving out is a magic wand for all that, but I doubt it, esp if H is taking on a huge parenting role in addition to his full time job, his business, his sport, wanting to start new sports, wanting to date or already being in a R, etc.
I guess maybe this is what your C was sort of guiding you towards. Less focus on your H. If your H has to work and WANTS to focus on his business, sports and a new R all of that is his to own and organize. As his single parenting duties increase he will find that he can't do it all. In a way you are enabling him to have a very easy separation. I am not suggesting for you to be ugly or nasty to him but let him try and do all that along with being a single parent. He might realize rather quickly the grass isn't quite as green as he thought.
If the two of you were to divorce I would gather since he is the income earner his work schedule would be considered when custody was arranged. While I agree the cycles of his work are rather inconvenient for custody arrangements right now it is what it is. I am not minimizing that it may be difficult for your children but some concessions will have to be made as your H must continue to earn an income.
I know you will worry and miss your children greatly but your H seems to have a very romantic notion about how simple it will be to keep all these balls in the air (work, side business, sports, single life and single parenting). The only way that bubble will burst is by letting him experience it. On the bright side of all of that it will give you three days a week to really buckle down and get some work done so your income becomes more stable.
Yes, the transition of more overnights would be brutal for me. That's why I wish that there was more guidance on what IS right for the children in a situation like this.
I don't have children myself but maybe there is no 110% concrete right answer and a bit of trial and error will be necessary to find a balance.
I guess the feedback that I'm getting here is to mostly let H have as much overnight visitation as he wants, then to insist on scaling back if there are negative impacts. I will have to seriously think on this. I agree that it would be good "DB strategy", but I don't know if it's good strategy for advocating for my children as all current arrangements are likely to become cast in stone legally. I don't think that I can trust H to acknowledge negative impacts on the kids.
If you are that concerned about setting a precedent with custody why not at least consult with an attny before you agree to anything. You don't need to tell your H about the consultation nor do you have to put anything in writing or file anything. Simply look at it as an informational meeting. You seem certain your H has gotten some sort of legal counsel. Why not do the same for yourself?