I think that's a really interesting idea to monetize the game and keep players happy. Having character limits can be frustrating, and paying a small fee to unlock more slots is a great solution. The idea of having different tabs for different seasons is also intriguing, and it could add a fun new element to the game.
On a separate note, have you ever heard of
solitaire cash reviews [joywallet.com]? It's a website that reviews different mobile games and apps that allow you to earn cash rewards for playing games like solitaire. While it may not be directly related to your idea for the game, it could be a fun and easy way to earn some extra pocket money in your free time.