Start the DC/DC assembly with the resistors and the capacitors. All the assembly should start with the lower height components. Mount a socket for the IC, then go to soldering the TO220 packages (mosfets and diode). These components are connected directly to a copper plane, for this the soldering iron temperature should be quite high (400-450 celsius degrees) in order to have a good junction. Mount at the end the inductor (remove the isolator with high care) and the input/output capacitors (470uF, 63V). To test the circuit, power supply the circuit with 12V and with a light load measure the output voltage: set via P1 the right voltage and check that there are no components with high temperature. Start to use the DC/DC converter, with attention to use "normal" components for power under 100W and "selected" components for power over 100W (see schematic description).