A camber kit might not be necessary, but you can get one anyways if you don't want uneven tire wear. But you might rub if you were to return everything back to OE spec.
unless you got it aligned, you dont "know for sure" that youre running -3° in the rear. yea, itll look like you have camber, but that doesnt mean you have -3°, unless you have a print out telling you what you have
agreed with everybody go get alignment sheet and not every car is set a 0 degrees some cars are set more positive and some more negative just get a sheet and go from there