I've secured the league so do I automatically move from Rookie to Pro or is it based on current level?
Also, do cars keep their stats or is a new season a clean start?
Once the season finishes, you will automatically be promoted to the Pro tier. There is no minimum level needed for promotion - you just have to be within the promotion zone at the end of the season.
Car design is reset at the start of each season. Your start-of-season design is based on the amount of stars your CD has, as well as their strength and weakness.
