A single Galtian superman could restore everything using the sheer force of his will and intellect. All that’s needed is a small, robust central government, a police force, a subdued labor force, gold preferably in bullion form, and a simple user manual.
I’m a pretty capable guy with a good understanding of physics, chemistry and engineering. Given enough time I could probably make any of the devices you see in a mid 19th century setting. Think Steam Punk. I’m sure I could get a group of about 50–100 people to that level.
Anything beyond must be left to younger and more capable hands.