How many cards should i put in a deck? (for standard and tournament play)
Always 8 for everything
Morecontrol over your draw
+1 what he said. Can't go lower, and packing more only dilutes your chances of picking suitable combinations.
8 is the minimum allowed and most players use 8 but sometimes in DTs 9 card decks are used to get a higher * count whilst only using low * cards (though with the DT changes this isn't done as much).