They go back into your hand, so the best cards to sacrifice are ones with good ETB/LTB abilities, preferably cheap ones
Choosing a higher value for X lets you pay more mana and thus spend more colors of mana to cast it
Whenever a player successfully knocks out one of their opponents Pokmon, they can take one of their six available prize cards, with the other player needing to put another Pokmon card into their active slot
Adding Lightning Bolt is going to require adjustments to the mana base
As the format progresses and we learn more about it, these will absolutely change, so take these picks with a pinch of salt, but I hope that this can serve as a baseline for the set as we get started with it and you test yourself on the Secrets of Strixhaven draft simulator
We can see the headliner for Edge of Eternities Sothera, The Supervoid