Design dc-dc converter for adjustable voltage
The datasheet recommends the design number 1 with the bias connected to Vout.
However, this is not a typical USB PD, as a single design should be able to deliver 5V/9V/15V/20V up to 3A with a communication protocol to communicate with your load to define which voltage is needed.
It looks like to me as 2 different design as you will need physical modifications for the 5V and the 20V.

For the Inductor value, it depends on the footprint, if it's the same, no matter, you can decide the values later, but bigger means less ripple however higher Rdc and price obviously => trade off 

Concerning Rff and Cff, this might impact your compensation, you might want to place the footprint in your layout, if you don't need it then keep it NC.