I know this is a really stupid question but I have to ask it. This is a stand alone game you dont have to buy boosters for it just expandions. Is that right.

Yeah. You get 4 decks with the coreset totally able to make for interesting games.

...also, when new sets come out, they are all the same. Buy one pack and you have at least 1 copy of all the cards of the set. I believe when the next cycle starts they will be coming three copies of each card to a pack.

And you do not 'need' these other packs, no more so than you need any of those other expansions for games, like Arkham Horror's expansions.