You have to make a trade
No, but you can in yellow
You start your game and get 1 starter then trade it. Then start the game again and pick a different starter. Do the same until you get all of the starters from Pokemon black and white.
Trade for them.
you'll needcheats.
You don't.
you have to trade them
The gender ratio for a starter pokemon to be a male is higher than the starter pokemon to be a female but it is possible to get female starters.
No man no man
trading or a game shark would do it
after beating alder and seeing or catching all Pokemon
For a list of all known Pokemon, see the related link.
No. Pokemon can't be traded from Black/White to older games at all, even if those pokemon existed in those older games.