The featherwing assembly is very simple because it includes very few components including headers, capacitors, an LED and a couple of diodes.

After assembly, the first step was testing: 

The board could be powered using an FTDI adapter board or by stacking it on top of a board from the feather ecosystem. 

The basic functionality of the board has been verified. I am able to power up the board and make the cellular module connect to the network. 

Cellular module connected to the network: