If you allot 510 EVs into it, then it will not get any EVs from further battles. It would be safe to fight any Pokemon you please. Also, if you go with the double battle route, either (1) have Smeargle have 510 EVs, or (2) kill Smeargle before beating the enemy.
Yes, the Trainer Cafe trainers are random... But Maylene appears there, and you can learn Spore on that day.
Yeah, I'm already doing that. I'm gonna be getting the moves after the EVs are all done. I was just getting some help beforehand so i can do it right when i finish.