Welcome to PokéCommunity! Register now and join one of the best fan communities on the 'net to talk Pokémon and more! We are not affiliated with The Pokémon Company or Nintendo.
You need a better physical wall then Torterra. Steelix would be a good choice, even a Drapion aces Torterra's Defence. and don't have both Empoleon and Regice as special walls, they're too similar, for the love of all that is holy use a blissey!
Don't worry about it, I've seen people take out Mewtwo with a Drifblim with horrible stats in competitive play. If you're determined enough you can win anything.
Yes, it does get dark at night in D/P. (As well as having two more 'times of the day'; morning and evening which also change in-world appearance, or at least evening does.)
Those ones aren't easy to get, The only way I know is to buy them in Pokemon Battle Revolution and Coliseum (XD might have them to) and them transfer them to your DS/GBA.