I have not read this whole post but using a fan center to run a oil furnace is rather simple. Use the black and white wire to power the fan center from the oil furnace. Tie the red wire in with the black wire used to power the fan center so it has constant power on the red wire. Cut the wire to the fan motor and run it through the relay. The black wire off the relay needs to go to the fan motor and the brown wire needs to go to the wire that normally supplies the power to the fan. This will allow the existing heat to work because the black and brown wires are normally closed. Now, using a three wire thermostat wire conect the new thermostat to the relay, c to c, r to r, w on the thermostat to g on the relay. Now when the new thermostat calls for heat it will activate the relay and send power from the red wire to the black which will turn on the fan. The brown wire will be disconnected when the relay is engaged so no power will back feed. Hope this helps.