1. For the challenges, playing the first one each day starts the clock for refill for next day availability. So play the first one each day as early as possible to get the refill quicker.
2. Unless your decks are strong enough to win every level throughout the event, you may be better off not winning the early ones so easily. You'll get more tokens (and thus more rewards) for taking 20 tries to get to level 21 than taking 7 tries at 3/level with perfect scores. Eventually you will hit a wall where you start to lose. Better to have played more rounds before that happens.