RE: Ash's Pikachu
Ash won the orange island league, which isn't like the main leagues. Also, once you have trained Pikachu with 510 EV's, and you battle red for the legend ribbon, if I remember correctly it won't earn more EVs once it maxes out. You could battle Red and have Pikachu not be sent out at all if you want to preserve EVs. Do you think Red's level 88 Pikachu counts as an actual "Ash's Pikachu"? My noob friend used an action replay and caught that Pikachu in a Masterball. One more thing. Since Ash's Pikachu hates pokeballs, I think it should be your walking Pokemon all the time in SS. I know of you go into some places (Global Terminal, Battle Frontier) or heal at the Pokemon center Pikachu would have to go inside it's pokeball. You could heal up at the house on Route 27/28 (I forget which, it's the one leading north to Victory Road), where you techincally don't have Pikachu go inside it's pokeball.
To keep in the tradition of Ash's Pikachu, you should try to keep t out of it's pokeball at all times (or just while training it).