Attempting to determine power consumption
The way of your calculation is basically correct.

Of course, the devil is always in the details.
Normally, one calculates a "typical" outcome, and a "worst-case" outcome. For those calculations, you'll need the "typical" and the "maximum/minimum" figures from the data sheets.

A few factors to consider:


the battery might have a capacity of 2000mAh when new, but this will most probably go down as it ages,
the battery capacity highly depends on the temperature; if you want to use it only at room temperature, it might behave much better, but outside at -25C degrees, the capacity might be only a fraction of the normal,
the consumption of the components might as well change depending on the temperature,
the consumption of communication peripherals usually highly varies according to the state of the communication (active, waiting, standby, etc).