Since you are using an alternative cost to cast a spell from exile this way, you can't pay any other alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, you must pay those.

The experience counter goes on you, the player, not on Aang. You will keep that counter even if Aang, Airbending Master dies.

Lands exiled this way cannot be played from exile. (Lands that were animated by earthbend will be returned to the battlefield tapped when they're exiled.)

Tokens exiled this way will cease to exist and cannot be cast.

If the spell you cast has in its mana cost, you must choose 0 as the value of X.

To airbend one or more permanents and/or spells means to exile each of those objects. For each card exiled this way, for as long as it's exiled, its owner may cast it from exile by paying rather than paying its mana cost.

All experience counters are identical, no matter how you got them. For example, the last ability will count experience counters that you got from the second ability, from another ability, from another copy of Aang, Airbending Master, and so on.