To face Thundurus in BW2 is impossible as you can only get it through trading with White.
You need dream radar so you can't get it in black 2 or white 2.
you need thunderous and tornadus then go to undella town and find out how you get to his shrine. when you do he will come out level 70 so be prepared.
no victini is not, thunderuos is not and the 2 that look like thunderous is not. zecrom is in the black stone in the 2nd gym leader's museum but will come out for you when you battle n in his castle
you cant really catch him you must trade him from black/white. hope this helps!
4 because the sell pokemon white and pokemon black and know they sell pokemon white 2 and pokemon black 2
Yes
There are 300 Pokemon in the Pokemon Black 2 and White 2 Unova Pokedex.
Route 20 does not exist in Pokemon White, but does in Pokemon White 2.
Reshiram is not in Pokemon White you need to trade either with Pokemon Black or Pokemon White 2.
White Kyurem
No, Pokémon cannot walk with you in Pokémon White 2.
You can hack Pokemon White 2 by using an Action Replay.