1. No. Your players will lose one star when you level up to a Level 2 manager next season. If you don't level up to a Level 2 manager (i.e when you finish as place 8 - 14 in League) your player won't lose a star.

2. Your player gain experience but they won't get as much experience as in a League, Cup or Champions League match. Training is way better.

3. -