we already have this big ass radiation belt around earth
it won't build up around the atmosphere or in the atmosphere (because they don't loving use them to get out of the atmosphere) that's not how it works.
and you're not constantly detonating nukes to stay in orbit
you use it to escape orbit, that's it.
That would be in theory but we always have that starfish that does whatever they want.
no there wouldn't
as others have mentioned not everyone gets control over the spacecraft
Uh, I don't think those are supposed to be interstellar. This Project Orion thing was going on before we even landed on the moon.
plasma drives can be used to escape our solar system easily
it'll take forever though
which is why the nuclear pulse drive would be used as the main propulsion and plasma drives used later on in the mission (don't quote me on this, i'm not 100% sure).
also in regards to the emp thing
orion uses low yield explosives iirc (say 1 kT bombs, not modern nukes with much higher yields of 1-2 mT).