MLS starts to join in the next round, so we could feasibly draw New England which would be very weird for me personally as I have tattoos for both clubs on me.
The $10 is to upgrade to the Switch 2 version, sorta like PS4 to PS5 upgrades. You can play your game just fine if you don't care about the upgrade.
Your cart will need to be used as it's basically the "license check" to play your game.