No clue on adding paddle shifters, but since the car's about 6 years old now, I highly recommend drain/fill the ATF and changing the filter. It's the official service interval by the manufacturer (ZF) and not Audi. I've used Valvoline MaxLife ATF for the past 3 - 4 years and it still shifts as smoothly as new.
Also, I don't know how fast these torque converter transmissions can change gears. But I guess if it's good enough for the Supra/Z4, then it's probably fast enough for the A5.