I am adopting my nephew from my sister. I have a lawyer I just need to know what else I need to do (home study I don't know if it applies to private adoption) etc.. And how much will it cost?

You will only have to do what the court ( judge orders) the attorney should be famailar with what this judge may require. Normally just the babies mother and father signing off on their rights to the child is all that is needed. In a private adoption.