How to calculate average power consumption in mAh?
how I would calculate every stage together


Using
$$ 1 \text{ mAh} = 1 \text{ mA} \cdot 3600 \text{ sec} $$

you can calculate the average as:

$$ 0.05 \text{ mA} \cdot 3473 \text{ sec} + 56 \text{ mA} \cdot 120 \text{ sec} + 0.44 \text{ mA} \cdot 6 \text{ sec} = 1.9 \text{ mAh} $$


  get an accurate calculation of how long the battery would last


You can only use the number above to make a crude estimation how long the battery will last.
One reason is that for a high amperage the battery life will be shorter than the product mA times supply time.
Another reason is that the battery will self discharge.