I’m glad you are trying it out. As for the lip bends you may have some trouble going a whole step down … So try a half step the first time ( C , B , C instead of C , B , Bb , C ).
Listen to the tone or sound… Try to avoid getting an airy sound, it will probably get airy but try to keep your lips as close as possible. This will help prevent an airy sound as much as possible.
-Yes your observation about the focus and speed of air having to do more with upper rage than the amount of air is spot on. The amount of air deals more with volume/loudness.
Just stick with it, and remember these are all just exercises not musical Etudes. It’s like going to the gym to work out, not playing a game with the team or performing an ballet ice show.
Let me know how this all pans out for you.