In the case of tournaments, I feel like the people should dedicate around 3-4 hours of their day if want to participate. Tournament is something dedicate time for. Yes I understand this game is completely online. but waiting for other person to finish their turn can be kinda annoying. I don't know how many people should be in each tournament because we have no clue how long the usual game lasts when playing at decent speed. From one advanced video they have posted, game lasted 11 minutes, but they knew and understood how cards were played and the rules and why everything went down.
If games do take say around 20-25 minutes, shouldn't really take that long to do a tournament to do. The one thing that can help in keeping games from going to long (in terms of 2 people in constant play) is the morale system that is another win condition.