Original duals are at their best when fetched early, securing both colors without sacrificing speed or life
But Im a writer, not a mathematician, and will let someone more experienced explain that particular formula
The wider your board gets, the more effective each spell you cast on Zada is
If that creature's power is 2 or less when it enters the battlefield but becomes greater than 2 after the ability triggers, the target creature will still get +1/+1 until end of turn
The other big lesson is you should Inquisition of Kozilek before you Thoughtseize
Elspeth can come down in the mid-game since she costs five mana, either establishing a board presence with her first two abilities or destroying a problematic creature of your opponents, making her a control players dream planeswalker