The technology is not unproven. As mentioned, the Bikini test took out the traffic lights in Honolulu. OK folks, those ran on relays, which are about as EMP resistant as electronics get.
For a long time, US military doctrine was that WWIII would probably start with a Russian nuke about 100 miles above Kansas City. That would affect most of the country, though you'd probably want two more, one for the east coast and one for the west.
Depending on the time of year, feeding the population isn't all that hard, conceptually. We could feed ourselves if we could get about half the population out in the field, wielding hoes. Even though that's conceptually easy, it would be very hard to mobilize: no phone, no TV, no internet, minimal transportation, not enough horses to replace tractors.
Electronics definitely do not need to be plugged in or turned on in order to be fried. If you keep them disconnected and in a grounded Faraday cage, they will probably survive.
OTOH, it will probably be a wonderful opportunity for those of us old enough to have started our careers in a vacuum tube factory. Dust off your Heathkit AT-1....
