Iroh learned absorbing and redirecting lightning from the waterbenders.

do you think he can learn other moves from earth benders, air benders or more techniques from water benders?

i would like to hear very creative ideas.

Hmm...I can't think of anything right now, I'm kind of sleepy...

But I'll give you some tinder to work with.

Jeong Jeong's wall of fire is similar to that of earthbending, amirite? so speaking from the source I would study jeong jeong for earth bending.

As for firebending relating to air, I would suggest rewatching "the avatar and the firelord"
Study Firelord Sozin absorbing the heat from the volcano and releasing it into the air. More of a repressive fire tech. but still...

And Azulas little escape in the ball of fire would be considered an air idea.

Just use some of these Ideas. Think about them in a way Iroh would and you may find there is more to the move itself than meets the eyes. A fireball shell could have more than one purpose.
nice.

The Earthbenders feel a connection, a strong one, to the earth. The Firebenders could feel a strong connection to heat, and the sun.

The Airbenders confuse their opponents. The Firebenders could throw fire all around their opponent, encircling them in a circle of fire.

The Waterbending technique, is, well y'know.

And there you have it (well, it's the best i could do).