Calculating power consumption of optocoupler
You're quoting the ABSOLUTE MAXIMUM RATINGS for \$P_{diss}\$ at the input and \$I_F\$. You should not use these parameters as design parameters or actual values, but consider them as values which should not to be exceeded. Like the footnote says:


  Stresses in excess of the absolute maximum ratings can cause permanent damage to the device. Functional operation of the device is not implied at these or any other conditions in excess of those given in the operational sections of this document. Exposure to absolute maximum ratings for extended periods of the time can adversely affect reliability.  


Regarding your calculations: \$I_{in} = I_F\$ for all situations, so, you should use the same value for the current to calculate the \$P_{R3}\$ and \$P_{opto}\$.

Then, yes, 


  The consumed power of the input circuit would be $$ P_{tot} = P_{R3} + P_{opto}$$
  
  Is it best practice to choose a the highest resistor which still guarantees that the opto functions as intended?  


Yes, like shown in Current limit resistors for Optocoupler controlled Mosfet
When you use a resistor value that just works for the absolute worst situation, then it works for all situations.
For linked question, a minimum current of 2.5 mA was required. It cannot hurt to increase this to e.g. 5 mA as the maximum allowed forward current is 60 mA. But still, there is no need for as the worst situation is already covered.