The Super Cup is just the 1st and 2nd place of La Liga versus the Winner and Runner up of the Copa Del Rey.
Not sure if EA ever made the weather correct in Spain. I know in 2019 I did a La Liga CM and the regularly tried to have me play games in the snow. I always just changed the weather on my own. I even went as far to look up typical weather for the various cities.
La Liga it's common practice for players to get release clauses. I think almost every player has one. Probably doesn't matter if you only plan on playing a single season though.