In a statement, Target said that it would "temporarily suspend the sale of MLB, NFL, NBA, and Pokmon trading cards within our stores," but would still sell them online
To build a new deck (Magic Assistant has no concept of a cube, but functionally a cube is arguably no different than a deck), right-click on the Deck category in the Card Navigator panel, then select New to create a new deck
Mana abilities dont use the stack, and other activated abilities of lands arent spells even if they use the stack
Emptying out your library should be turned into a benefit for you, and you have several options
Urza's Incubator is another one that might be right at home here, I guess it depends though it wouldn't really net you much value over say a Worn Powerstone unless you are playing multiple rats on an average turn