I am a child of a divorced family and am also currently going through custody issues over my step daughter. There are many things to consider and make sure you have worked out.
First, do you and your soon to be ex have a good communication and relationship still. If not then you will want more of the custody stuff set in writing, but if you know you will still get along well then you dont have to have as much.
Definately have the taxes, child support, and set holidays in writting. If you know you want specific holidays every year and he wants others than have those in writing too. If you dont then you will be expected to switch every other holiday every other year and not following the papers could come back to bite you in the butt. Also, have birthdays put in the papers so there is no questions later. You will want to figure out summer vacation and winter vacation also. If you are living in the same town then many states will give the noncustodial parent two weeks visitation (the child stays with them for the while time) however these two weeks usually have to be split up and not back to back. If you will be in seperate states and not doing everyother weekend then it may be the whole summer. You will have to decide between the two of you.
As far as health stuff, we have found that it is best that both parties be required to have insurance on the children. Also, whoever has full custody (if you do not plan on joint custody) needs to have it state that he or she be notified immediately if the child has to go to the docotor or er. In our case things are really messed up and therefore, the biological mother is not allowed to make any medical decisions without my husband and i present or without our permission. you do not want to go this far unless really neccessary though.
All these ideas are things you should think about even if you do not follow them all. If things are going to be really messy there are other things you may want to think about. I hope you divorce does not get that bad; however, as I mentioned I have been through a messy one as a child as well as am currently dealing with custody of my step daughter which is messy therefore, I unfortunately know a lot of the worst that can happen. If you want more ideas or information you can email me at ____@____.com
best of luck
B.