Kades, I usually put dried porcini in my sauce. I don't see the need to rehydrate them first, I just break them up and toss them into the sauce dry. There's plenty of liquid to rehydrate them during cooking.
These mushrooms do not make my sauce brown.
Between the sauteed onions and the sauteed tomato paste, I get enough sweetness to cut the acid. I never add sugar.
Occasionally, if I encounter a particularly acidic can of tomatoes, I have resorted to using the smallest pinch of baking soda to neutralize the acid. Works great.