Either way, and mana symbols are represented on the land somewhere, even if it's on the back half of a transforming card
Saheeli, the Gifted is a fine commander, with her ability to add a bunch of mana with her second +1 being especially scary, but she suffers from the fact that there are a bunch of artifact-based Commanders available, including the extremely powerful Breya, Etherium Shaper, so being "fine" might not be enough to pick Saheeli, the Gifted as your Commander over other options
Sliver creatures add bonuses to each other, adding up until they create an unstoppable army led by Commander Sliver Hivelord, who makes each Sliver indestructible
One of the first decks to come out of this utilised my next pick to great success: Tolarian Academy
(See rules 800.4a and 800.4c.) If a phased-out permanent phased out under the control of a player who has left the game, that permanent phases in during the next untap step after that players next turn would have begun
It will release on August 12