Free level 30 Resistance char question

You activate the mech itself via a skill xP not an equip.
Those Mech parts are simply for extra stats, you function perfectly without them, and the first set (Copper) starts at lvl 50 anyways.

Of note, you will actually get the Copper Engine given to you in a new quest at level 50. It pops up as a bulb, but you must go to Resistance HQ to pick it up.