Should have already.
No
Child support is paid until the children are 18.
Until/unless you are determined to be the child's father, no.
A childs mother must file a petition for child support in the local family court.
Welfare
If he is married to the child's mother the decision is theirs to make, but if he is not married to her the mother decides the child's last name.
If the judge in the court with jurisdiction feels it would be in the best interests of the child to issue such an order, yes.
You can, but eventually the court will question what you are doing.
Child support and child support arrears are paid to the parent of the child. If you are still receiving arrears after all these years, you might consider visiting the county attorney where you live and filing aginst your son's father. Depending on how much is owed, there are several actions that can be taken, including suspension of driving privileges, attachment of assets, property liens, and incarceration. In the meantime, however, the funds must come to you directly and cannot be sent to your son.
The childs' father, married or not. Your relationship to the father is irrelevent. The father is the first on a long list of family members. Create a living will if that is not acceptable.
No, it will have no effect.
It isn't the birth father, no one will ever change the childs birth father, but he will legally be the step father,until the divorce comes through.