How much energy would be required to make things out of metal using this process?
Not possible, as the metal is opaque. The resin is mostly transparent, and the UV/blue light that excites the polymers to harden can pass through, and won't trigger the hardening. unless it's focused down to a certain intensity.
You could use the polymer 3D printed model for a mold positive for metal casting though.
There are several sorts of metal 3D printers though. Ones that print with the plastic weed whacker line, but it's actually glue and metal powder, and you bake it in a kiln. Ones that spray glue on metal powder a layer at a time, then you bake it. Ones that shine a laser on the metal powder melting it together layer by layer. And ones that use a laser, gas flow, and metal powder coming out of the nozzle to build up metal parts in empty space.
SpaceX makes some rocket nozzles with the "shine a laser layer by layer on metal powder" method, so the parts can be quite tough.