Congrats on the day being good so far ! YOu have a full plate for sure . I have been thru that route with the kids going to their Dad's, only weekends tho. He wasnt the greatest Dad in the world for sure (one reason I left him), but I finally decided to make peace with myself and accept the fact they were "Half" his, and like you, I would be their "safe place to fall" if their time with him did not go well (it usually did, I just never thought anyone could be as good a parent as I was !!
My son's are now grown, and they turned out just fine!

You have quite a list of things you need to do - perhaps you can make a list of what has to be done first and so on. Check them off as you are finished.

A Support Group sounds great and you going alone the first time might even be the best way to do it. Then you can talk to your children about what to expect.

Good luck, and take care of YOU during this time !!