Welcome, Mr. Nobody!
@Mr.:
Since there is no AA or defending land units what happens to the air units on that territory? What if a territory only has defending air units? Can they be destroyed by attacking air units. Are they presumed on the runway or scrambled?
Units always defend normally in general combat unless the rules specifically state otherwise. Also, any kind of unit can hit any other kind of unit unless the rules specifically state otherwise.
@Mr.:
How many times can air units press their attack on defending land forces?
As many times as they like.
@Mr.:
How many times can a bomber attack an industry or base?
Once per turn.
@Mr.:
If air units attack a territory that has an AA,industry, air and naval bases do all the AA guns get to fire in defense of the territory? Is it the same for a strategic bombing run or does only the targeted infrastructure defend with AA?
AA guns fire only in attacks against combat units in their territory. Facilities use their AA fire only in strategic bombing raids directed against them.