You might get something out of how frequently there are announcements on this channel. That's the only real info you're going to get out of this unless you're in a very select group.
Land based would take maybe twice that much.
Effectively the world has been 30 minutes from 'dead' since the 1960s.
Basically, you would run out of water, and even if you have clean water you would still run out of food, even if you survived the strike and the fallout. We cannot actually live without major transportation hubs to deliver food etc., which by necessity are located in or near the major urban areas that would be destroyed in a nuclear war. That, more than anything else, is why the US and USSR ultimately abandoned "civil defense" and focused on "deterrence."
It’s why Hiroshima and Nagasaki were repopulated so quickly.
But yes, good point regarding the rest of the infrastructure.
Rebuilding society would be very hard.