What is your favorite exercise for weight/strength training?
I enjoy yoga which is more associated with flexibility training.
What is a good length of time per day to do yoga for flexibility?  I would like to incorporate yoga into my exercise routine.
20 minutes per day is sufficient enough to increase flexibility.
Any other benefits you get from doing yoga?
Hatha yoga is a type of yoga that emphasizes physical exercise to master the bod and the mind.
That sounds like that will help with breathing as well.
Yes and Zen yoga is also really good for that.