I think that this site can answer most of your questions.
http://www.healing-arts.org/children/ADHD/treatments.htm
In terms of mood, depression, anxiety - in my opinion, it depends on what is causing the above. Many studies have shown that depression affects a number of people with ADHD/ADD. I would suspect that if the person understands what ADD is doing to them and is then able to more effectively cope with it by either behavioral modification or meds, then the depression would get better (as long as it is caused by the ADD).
The amount of time the person is on the meds varies on the needs of the person. That seems to depend on the coping skills the person learns and the environment (school, work, etc) that the person is in.
Hope this helps, I can recommend other sites or books if you have more questions.
Best wishes.
I was diagnosed with Narcolepsy/ADD about 30 years ago and have taken Ritalin an adderal without a problem.