1. 470 ohms empirically determined to give best distortion performance if memory serves me.
2. Best guess is 1/8W, maybe less. The voltage swing will be less than rail-to-rail p-p over 470 ohms so that's 9.6 mW worst-case for a 3V supply.
3. It's a CMOS logic output (per DS Figure 20). I don't think impedance matching really matters here, just buffer and low-pass filter the signal.
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