Placing a 5ton evaporator coil with a new one. How much oil needs to be added since the new one won't have any charge?

You may not need to add oil to the system. After removal of the old coil drain it and measure how much oil it contained if any. Oil is not supposed to accumulate in the evaporator since it is supposed to travel back to the compressor through the suction line.

You will need someone to recover the refrigerant that is in the system and the copper connections will need to be brazed NOT soldered. Then the system will need to be pulled down with a vacuum and standard refrigeration procedures followed. I always add a liquid drier to the system for good measure. Note If the system has a drier located in the outside unit it will need to be removed before adding a new drier.