You get 100 gold when you reach level 10 with all the classes (when you unlock all the basic cards for each class deck).
You get 300 gold when you win 100 games in any mode.
I’ve won over 300 games and the only reward was at winning 100 games.
And there are daily quests that reward with 100 / 60 / 40 gold. It depends on the quest, how many times you have to win, bigger amount = bigger reward.
I think there are more gold rewards as you progress in the game, maybe at reaching level 20 with all classes.
If anyone has reached these levels or know any other rewards, please leave in the comments.