Some oils already have the additive, if so it will state so on the bottle.
Brand, what ever floats your boat. I can't think of how many 9" axles I have seen with 300, 400k miles on them and still filled with what ever came out of the factory. and it sure wasn't anything fancy. The lubricating requirements are not very demanding in most applications. Being Ohio, I would look for a 75W90 oil. That will be thin enough to flow good on those cold winter mornings. I save the 140W for tow vehicles in Arizona where the oil gets super hot, then I go synthetic as well due to the heat.
Fill to the bottom of the fill hole.