I wish I could get your H in a dark corner and kick him. But I think I'd be competing for that pleasure with a lot of people.
You do need to stop worrying if you're impacting him, but that is a process. Just work towards it. You are about to go through a process (the divorce) that is going to hurt much more than all the cr@p that's come before. Use it to fuel you. Whatever BS he pulls, whether it's the show of the perfect father or what not, just use the frustration from it to push you forward. It really does get better. And he will lose patience with trying to put on the act and revert back to his real self.
If you're worried about the effectiveness of his impression management... you've already had friends tell him that they can see through it. It's going to be a case of too little too late. You're worrying about that is just a symptom of how much credibility you're still giving his claims for why he pulled all this on you. He has no excuse. He just is looking for one and has decided to blame-shift his cr@p onto you. YOU DON'T SUCK AT ALL. He does.
FWIW, several years ago I had a friend going through a lot of what you're going through. She had four little kids and her ex, who had never done much of anything, pulled the old 50/50 custody thing on her. She reached out to people who had known her through her life and asked us to write letters describing what we'd known of her and him as parents. She got MANY letters of support, and yep, she kept her kids. What he's trying to do now is known as TOO LITTLE, TOO LATE. Because a guy who walks out on his newborn child has a handicap in the "good father" department that can't be overcome by carrying the baby around at a soccer game. People are likely looking at him thinking, "He must not see much of his newborn otherwise since he's taking FB pics with hoes."
You will be fine. Just relax into the roller coaster and have a strategy that will help you quit giving him so much space in your head.
I do agree that if he offers to help, you should take him up on it. You aren't going to get a lot in the future. Take it while it lasts, so you've got the energy to do what you need to do. Even if it's bitter going down, you'll be able to know you took the high road and didn't try to alienate him from the children. (I get it, I don't think my ex should get to have a good relationship with the children after how he hurt them, but that kind of thinking only makes their and my lives harder in the long run.)
Keep being mighty, T!!!
Me42, H40 D12, S8, S7 A revealed: 7/13 Sep 4/14; Agreed to D 1/15