I think one of the things you need to write into this contract of behaviour, Dusty, is that you need time off from your DS (obviously not in those words! but ykwim). So: if you do ultimately split, shared residency will give you that; but if you stay together, make sure you get at least one day a week off.
I think the counselling session is a good idea but agree that you need to play things close to your chest. Make sure it is all about what you need for things to ever work out between you and your H. Keep quiet about anything else - do not let yourself be pushed on what might happen if he fails to keep to his end of the bargain. And make sure you get the solicitor working on the financial agreement. At this first joint counselling session, make sure that your H gives you space to talk - if he monopolises it and makes it all about the affair, you will be lost. You need to make it about what YOUR needs are now.
You also need to remove any level of rose-tintedness from this situation - you need to think in cold hard facts, take the emotion out of it completely so that you can deal with the practicalities - but only while you are dealing with stuff. Be hard-headed, as though it were a business deal - and then at the end of the day, when you are on your own and not trying to sort everything out, you can deal with the emotional side of things.
I think you are doing brilliantly, and I hope you get the right outcome for you and your family - but to do that, you need to play hard ball now, without letting your H know what your game plan is.
And I know I'm using these metaphors, but remember this is NOT a game and I'm not suggesting that it is - this is a life strategy to get you through the next however many months/years.
I am being very dictatorial in this post, sorry! Just trying to access your cold hard-headedness :)