Does Goku happen to have kryptonite on him?
Nope, they're just fighting each-other.
As for the talk about ki, ki is indeed derived from basic biological processes like eating but it's also taken from simply having a strong body, it's restored by rest (so similar to sleep, maybe, which we know nothing about), and it's at least partially spiritual. It's been shown in the show that having the right emotions in the right amounts can increase someone's power tremendously - not just ki, but also speed, strength, and durability, though the latter three's increases could be derived from the former's increase. See: Vegeta (Battle of Gods)
...Yes? It's a somewhat major plot element in the Buu arc...
It is never a major plot point in any of the arcs. It can't even be called a plot point, seeing as her biological nature doesn't influence the plot in the slightest. I will say that her ki source is NOT biological because it can't be sensed by the....what are we calling them again? Z Warriors? Z Fighters? Main characters?
(Suppaman, on the other hand, Goku could whip one-handed)
Forget Goku, HERCULE could beat Superman! He broke like 16 of them with just one hand! Actually, that's the thing I like about Hercule. Compared to the Z Warriors he is absolutely NOTHING to them but he's actually a legitimately good fighter. If he were alive IRL he would actually and legitimately be the world's martial arts champion. Just compare him to normal humans instead of anime heroes.