As for the Nuzlocke question: Giovanni and the later rival battles are nearly impossible at lower levels, a they can not be adult soloed by a single Pokemon with a type advantage. I tried a Pearl run with no abuse of leveling, and was promptly destroyed by the first non-monotype threat I faced. I would level up a Pokemon by about five levels when you catch it to be safe, although that makes things fairly easy, which I need them to be to make sure that I get as far as possible for the sake of the novel I'm writing. In short, it all depends on how hard you want the run to be, but it will be virtually impossible without any extra leveling.