Single mode GT League (Gran Turismo Sport)

Hello. Today I read the news that the GT Sport was added single-player mode called GT League. I don't have this game, but I plan to buy. Have 2 questions:

1. To win a GT League - do I need to have a PS Plus subscription? I heard that it is mandatory for network racing (multiplayer), but like this mode should work as single player. I would like to be able to play it without PS Plus subscription.

2. How big is this mode GT League? I mean - it short or decent time? I'm not a fan of multiplayer races and I would like to buy this game just for the single player mode, but if you can go for 1 night, the sense in purchase is not. Write, please, who has already got acquainted with this mode.