Well, you'll either need to collect the cards from Arena booster packs for the sets they came in, or else directly 'craft' the specific cards you need using MTG Arena Wildcards - effectively tokens you can exchange for the exact Common, Uncommon, Rare, or Mythic Rare card you want, depending on the type of Wildcard
If you want to copy your Commander, either of the Sakashima cards or Spark Double are great
The archetypes primary guiding voice was historically great deckbuilder Mike Long who actually went on to win that Invitational with Keeper, albeit with both copies of The Abyss in the sideboard
6 Kozilek, Butcher Of Truth There's something of a back-and-forth debate about whether the Rise of the Eldrazi Ulamog or Kozilek is better
If your goal is to win tournaments or make money, then probably not