1. No, it seems like this is just cosmetic only.
2. Having players with a decent passing skill, and playing 'short passing'.
3. Attacking mentality will get you more goal opportunities, but will leave you open on the counter...even more so with hard attacking.
4. Yes it does benefit, if you want to gain the maximum skill points from training, but your players will suffer more fatigue, and also be at an increased risk of injury. - works best if you have red/green packs to spare.