I would like to know what happens in the courtroom for child support procedures NYC?

I am nervous about my court hearing. I am taking my ex for child support payments. I wanted to know if anyone knows what happens in the courtroom. Does he speak…do I? Is it based on his income? He has a son he is raising from a previous relationship but he does not receive child support for that child. In other words, he is raising him financially without help does that factor into how much he will pay? Will he be garnished (I do not want him to)? And if the judge decides an amount can he and I negotiate? I know how much he earns and his expenditures. I want to be fair. I understand NYC is an expensive place to live. I understand he is also responsible for ½ of daycare expenses. I guess I want to know if hypothetically speaking the judge decides he is to pay $850 monthly can I say I will take $650 or something like that? I do not want to suck him dry I just want what is fair and average for the baby. Finally my ex says once courts are involved we can never get them out and they will always mediate between us as parents, is this true? Anyone have a clue/idea?