First of all i recomend you go to this thread:
http://www.tv.com/avatar-the-last-airbender/show/28841/question-answer-thread.-frequently-asked-questions-updated-24-6-08/topic/13281-906762/msgs.html?page=138&tag=board_topics;page_last;6
before making a thread like this, because you will get critiqued for it. and if no one answers your question then make a thread
Starting from the top:
Longshot and Smellerbee from what was seen of them in Lake Loagai (excuse my spelling). probably settled down in Ba Sing Se because they wanted to start a new life for themselves, although they may have moved after learning that the FN took over Ba Sing Se.
I'm not totally sure whether the metal will play a key role in episodes to come. sokka's sword will play a key role because he will most probably fight in at least one of the new episodes. as for toph's metal, she hasnt used it after Sokka's Master.
Iroh's son died in battle at Ba Sing Se. Though how he died is never mentioned, i'm guesing he got crushed by a boulder or something to that extent
The disgrace that changed iroh's life (as mentioned many times in the series) is his surrender at Ba Sing Se.
Unsure.