I would either use Rotom or Mew.
I used Rotom for my first trip into this dungeon and got to the 64th floor before fainting. I'd say that's pretty decent for a first try!
Anyways, Rotom's a ghost type so in emergencies you could just go into a wall and attack from there. Also, Rotom knows Confuse Ray right from the start, which helps a lot.
Mew is great for this dungeon because he's got great stats and can learn every TM move, which this dungeon has a lot of. I could easily get to the higher floor levels with this pink destroyer.
The max amount of EVs you can have in a stat is 255, and the max you can have overall is 510. (In B2/W2, calling Bianca will tell you if anyone in your party's hit either of those limits.) As a result, you can only 100% maximize two stats and put minimal work into a third. You can heavily invest in all three of HP, Def, and SpD, but not maximally, and make sure they're all multiples of four (EVs work in rounded-down groups of 4, so having remainders in a stat is pointless; because of this don't bother adding more then 252 EVs to a stat).
It does not matter when exactly you use your EV-increasing items, as stats in Gen V are recalculated after every battle. That said, with a low-level Pokémon, you will have a hard time noticing any stat changes as you add EVs: at level 100, every 4 EV points adds 1 to its stat, and things scale uniformly for lower levels (so for example at level 50 you'll see a stat change every 8 EVs).
The Macho Brace (and related items), as far as I am aware, only affects EVs you gain in battle, and not those you gain through EV-increasing items.
Best Answer
No, the Pokemon Mystery Dungeon Games cannot interact with the main series games like Black/White 2.
I would mention however that some of the Pokemon Ranger series can. Pokemon Ranger Shadows of Almia for instance can transfer Riolu, Darkrai and Manaphy. Pokemon Guardian Signs can transfer an event obtained Deoxys.