1. Hard to choose, but maybe 451V.
2. Defensive mentality is good when you are playing against stronger opponent. Forcing CA is risky because oppo can break CA and then your defence will be opened for his CA. For me it isn't useful, I tend to avoid it. Offside trap works for me against 3ST formations when I'm attacking. I haven't combined OT with defending so far. You can't read OT in comments. If your defence with OT works, you will notice lower number of shoots in oppo's team which means that OT breaks his attacks.
3. I use long passing when I play against 5 mildfielders team or I'm defending. I can explain it in details if you want.
4. This is related with defending part of game, it is all connected there: fouls, oppo's shoots etc. Hard tackling is useful if reduces opponents passing % and number of shoots. If not, then turn it off just to decrease chance to get card. Usually you won't get card if your team plays good in defensive part of game so your player won't be forced to make foul to stop opponents. That is why fouls is important part of statistic, usually underestimated and forgot. Keep eye on oppo's shoots, if he has too much, change something.
5. I don't use arrows on all players, I think it is related firstly with strategy, then tactics. I try to counter every opponent so my setup is usually based after opponents. That means for example: If opponents has 2 wingers in team and they are in mildfield, I will probably use 4 wingers and red arrows on them.
6. Hard to answer, usually it is random, but good form helps, morale doesn't help much. I saw great form ST missing 100% chance and bad form player scoring.

For me most important rule of success in this game is:
If your players are out of form, formation, morale, quallity, tactics or friend's support won't help to prevent bad results!