Okay... The Battle Maison will require a more competitive team than whatever wild Pokemon you happen to catch. You can use nearly anything to beat the game, but probably best to have powerful STAB moves on each which run off of their best offensive stat. Like Waterfall on Gyarados, Moonblast and Psychic on Gardevoir, etc. You don't need to worry about getting them to level 100 as there's no trainers with Pokemon that high leveled in any of the gen 6 games thus far, but you can pass out EXP Power until you get it to level 3, give some affection to them in Pokemon Amie, turn EXP Share on, and then in Pokemon X/Y make use of Restaurant Le Wow for excellent EXP gain. In OR/AS, make use of Blissey bases, though you need to give them a day from when you load them in and will want to get a Level Release decoration so you can use the ones in other bases.i am trying to just beat the game, get them to level 100, and maybe do the battle maison, i am not sure yet. so far, i just want the moves for some of them.
When you're ready to dip into competitive breeding, check out Most's 6IV Ditto giveaway.