1) When you declare CAP you place them on the board edge facing a certain direction, they come in there and have to move at least 30cm before you get to turn. After that though, you're free to approach the target formation however you like.
2) After the approach move, see the FAQ for 4.2
https://tp.net-armageddon.org/tournament-pack/#aircraft3) Back of the formation is determined relative to where the aircraft were at any point along their approach move. If at some point they aren't suppressed and within range then they can fire at the aircraft.
4) It means you don't have to worry about the line of sight requirement to be suppressed, only the range requirement.
5) First strike happens every round, assuming the unit's in a position to use it (i.e. if it's a base contact attack they have to be in base contact at the start of the second round).