First, I am sure that there are plenty of skilled fighters that the Fire Nation can call on to fight during the Eclipse. Jun, Mai, Ty Lee and they could always threaten people of other nations to fight for them.

Second, wouldn't the Eclipse also effect Aang. Since as Avatar, he is a Fire Bender. Would it cause him to not be able to use the Avatar State, as he has to be Spiritually balanced. The loss of his Fire Bending would through him off balance, right?