原文An effect that instructs you to "cast" a card doesn't allow you to play lands. If the card exiled with Chandra's first ability is a land card, you can't play it and Chandra deals 2 damage to each opponent.
原文If you cast the exiled card, you do so as part of the resolution of Chandra's ability. You can't wait to cast it later in the turn. Timing permissions based on the card's type are ignored, but other restrictions (such as "Cast [this card] only during combat") are not.
原文Loyalty abilities can't be mana abilities. Chandra's second ability uses the stack and can be countered or otherwise responded to. Like all loyalty abilities, it can be activated only once per turn, during your main phase, when the stack is empty, and only if no other loyalty abilities of the planeswalker have been activated this turn.