If your in a room with a hundred different economize, you will get a hundred different theory's about economy and what is best. The same holds true with sport trainers, with regards to stretching and warm-ups. Have been to a few seminars. Every speaker has his (or hers) own personal slant on workouts, diet, etc. All their charts, graphs, white papers, etc differ slightly or big time. If stretching works well for you, than do it. But not to the extreme that it becomes more of any exercise it's self. And halt before that full stretch becomes more of an over extension of the muscles, ligaments, tendons and joints. That can happen way to much for some.
If I am doing leg work than usually 100, or so, Hindu squats does it for me. At times adding light Sissy squats into the mix. SS are an excellent stretch/warm-up movement. But one must get use to it slowly at first. Ham stretches with just holding the hands behind the back, keeping the back ram rod straight. And bend from the waist. Should feel it more in the ham's, rather that the lower back it's self.
Upper body usually starts with just hanging from a chinning bar to let the shoulders, back, spine, etc stretch out with the help of gravity. 60 to 90 seconds..rest a bit and than back to the hang stretches.There is a light combo that works for me also. Using 2 light DB's, start with straight arm pullovers. Bring the DB's back up overhead, and than do DB flys. Return to the straight arm pullover again, etc, etc, etc.. Alternate these pullovers/flys for 20 to 30 full stretch rep sets. Really primes up the upper body for the regular workout to come. Good Luck.