0) to my knowledge, in real life, all Junior matches are played in best-of-3-set matches.
Some pro tour matches (ie: Grand Slams, Davis Cup, and in the past, Master finals) are played in best-of-5.
You can choose to play in fewer sets than that, but the simulated matches are always done with the real sets.
But this reminded me that I should indeed scale up the tiredness when playing with fewer sets, so I just did that for the next update..!
1) I don't understand well again...
Even if you start at 0%, you'll get experience points to spend in training sessions to raise your skills
2) Stress happens on important matches & moments, and when playing against a weaker opponent: in this case, his level will lower a bit, but only to his opponent's level, at worst.
3) Your Short Term Form has to go below the little triangle to get fatigue effects ; your player will run slower & hit less strong in such a case
4) You can check a bit the TEM2 doc, it explains some of the concepts, but not all : https://www.managames.com/tennismanager ... _Game.html