Like most Magic: The Gathering cards, the value of Elite Archers depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Seventh Edition)
Magic: The Gathering is the original collectible card game, meaning it was the first game to combine the traditional collectibility aspects of baseball cards (i.e., cards with varying rarity, bought in randomized packs) with the imaginative play of games like Dungeons & Dragons (i.e., you get to fight goblins)
Keeping Kefka alive a whole turn cycle to use his ability again might be tough, but at least in black there's a fair few protection spells
While that's a question only you can answer, I'd point most players towards Bracket 2 or Bracket 3 to start
You get a large burst of card draw and pump depending on the number of auras you have attached to creatures when this enters
Combined with your Leader's effect reducing their cost, you will be able to nullify even big threats