how do you get rid of enemy fighters defending cities?
Attack the cities with fighters. Fighters have a stronger attack than defense, so you should win. Ok, I'll be precise, they have 2 defense and 4 attack.
if their air superiority ranges overlap will they dogfight until one dies?
They can only shoot down fighters/bombers in half their operational range. So, if a fighter had 6 operational range, they can only shoot down planes within 3 squares.
would starting by sending some fighters in on bombing missions be a goos way to go
Yes, you got it right!
As said above, use fighters first to attack other fighters. Just press the bombard button.
Does the Def Bombardment Adds up to the Def?like the TOW has 14 adds 6 = 20?or they just stay solo?
The defense bombardment doesn't add the defense to the unit, but it allows units to bombard before being attacked. They can knock off 1-2 hitpoints off the enemy before attacking. Of course, they can also fail.
By the way,talking about Swordsman,it reminds me of those Unique Units which plays a important part of the battle,which one is better,Gallic Swordsman Immortal or Legionary?
IMO Gallic Swordsmen is too weak for it's cost. It only adds one movement point for a whooping 10 shields (Which is enormous for the Ancient ages). So:
Gallic Swordsman
Legionary is great, but it only has three attack (The same as a regular swordsman). So there's not much improvement there, but I still like legionary's for the extra defense, basically like a 2-attack-point-hoplite. So:
Legionary
That leads me with...
Persian Immortal. A massive 4 attack points. A great unit for conquering. I personally find it too good, so I rarely play immortals.
So, top 3:
1. Persian Immortal
2. Legionary
3. Gallic Swordsman