Use a discrete power rated resistor for the “Resr” designator in the design on the front of the datasheet, unless you opt to use an electrolytic capacitor for your output capacitor.
Also, LCSC does not have the LM5166X, the fixed 5V output version, you’ll either have to get the part from somewhere else, or add in a resistor divider for the feedback circuit.
Exposed pads can be soldered using a standard soldering iron, the trick is to have the pad on the PCB exposed on both sides with a small hole in the center of the pad, you solder it from underneath.
What I do is I tack on each of the pins first, then flip the pcb over and solder the ground pad.
EDIT: nevermind, just realized the package is no-leads cancer, I would recommend using the LM5163 instead.