Hail!
3/ That's a good point, I'll try to add it, but maybe this way : bombing mission should do (collateral) damage to grounded plane (ie : that are not on intercepting mission). IRL you can't force your opponent to take off and face destruction in air combat with his Zero against your F-15, but if he don't, you can do damage to him on the ground...
But if his crafts already in the air on an Intercept mission then you can send an air stirke to take out his aircraft and clear the way for your bombers.
about your last point, I think I'll keep it simple (as it is). I don't want air bombing to became overpowered, it was too easy in warlord : the time you start to mass-produce fighter-bomber-tank you can then blitz any civ in a few turn
Yeah, but air bombing is suppost to be overpowered! When aircraft were invented all combat became much more fast-based war like in worldwar II, blitz was it, france couldn't withstand a blitz attack so they lost! See! Too fast!
Well, anyways, I think units should be able to get promotions that allow them to intercept aircrafts, and their should be, Boarder patrol, like intercept but only reacts within your boaders, to guard your lands and not have your craft killed fighting alongside some tanks in never-never land.
Oh, hey, here are just some more ideas for Air Combat.
Starting with buildings.
1. Anti-Air Gun Improvement. Has a chance to shoot down enemy aircrafts, comes with filght. Can be place along side any improvement.
2. Anti-Air Gun city Improvement. Has a chance to shoot down enemy aircrafts.
3. Helicopters should be able to land on Carriers. Or maybe a SeaKing Helicopter that can land on Carriers and attack like fighters but can't attack land units only sea and have a small range like 1 or 2 or 3, their good at killing battleship.Or they could be just like helicopters but just with a air bomb mission, so they like half air half copter, they weak but have 100%+ to battleships.
4. Precision Bombing, Modern Bombers should have an attack mode of Precision Bombing, allowing them to -when bombing a city- pick what they want to bomb.
City Improvement 25-50% Chance of hitting. Any building in the city, ANY.
Unit Garrison 10-35% Chance of hitting. Any unit in on the city, ANY.
Urban attack 25-50% Chance of hitting. Kills city size -1
5. Precision hit, Fighters should be able to have a mode where -If attacking a stack of units-they can pick which unit they want to hit. -25% normal chance.
6. Precision attacks should also be able to destroy roads and rails.
7. Bio-Attack. Bio attack is like tile bomb but it doesn't destroy anything, what it does is, if hits city, plus 1

. If hits tile, that tile can not be worked on for X turns.
Geez, I can't think of anything more atm, what to do you think of the new ideas? Sorry, I can't help myself! I'm a thinker!
Maybe you can have two modcomps, one with the blitzing air combat and one without!