Why not just share custody?
These people both lived in Manhattan. They both wanted to be involved in the child's life. The kid clearly loved them both. The parents were fairly amicable before the lawyers got involved. Why not save the money, maintain a cordial relationship, not upset the kid, and come to an agreement together? I'm sorry, but I have a hard time with the all or nothing stance that both parents took when it made the most sense to do this:
The kid has a room at mom's and a room at dad's. One week he lives with mom, the next week he lives with dad. They rotate holidays, split vacations, and have joint input in major decisions regarding the child. No child support to either of them because they both earn adequate money and have equal parenting time.