I am divorced, as well as my sister. My sister had a bad situation with her now ex, and 3 children. You have lots of great advice here. I've heard from children where the parents could work together or not talk bad about the other parent to have much appreciated and benefited from that. In my sister's situation, it was only 1 sided (her doing that), which I'm sure was challenging.
I'd like to reiterate that if you and your spouse can do it, to share a lawyer. I was able to get a divorce for less than $500 in 1996. That was lawyer and court fees. I was able to meet with a lawyer, all assets and decisions had been made by me and my spouse prior to that meeting. I met with the lawyer, and she helped me create the forms, and told me what I needed to do at the court house, etc. Our situation was "easier" because we didn't have children.
I do recommend some sort of therapy or support groups to help you through. If you are employed outside the home, check with your employer about an Assistance Program for mental health. The first couple sessions are typically free, and then there is a co-pay once you are aligned with a more permanent therapist. Otherwise, look for a support group through a religious entity.
Finally, I wish I had good advice for you regarding your husband being self employed. My sister's situation is exactly that, and it's up to self-reporting and tax forms regarding his income. Being self employed allowed him flexibility of identifying how much, or how little, he would make.
Hopefully, regardless of the situation, you both can come to agreement to be focused on your 4 precious children, and to work hard to overcome the emotions you have for each other to raise the children well.
Best wishes.