OK here goes.
As for the tongue arch I said TRY using a long aaaaaa sound instead of an eee. It is a more open mouth position and therefore a fuller sound. If you are playing 3 ocatves over high r# then you use whatever is needed to stay there. As for a specific vowel for below middle c, middle c to Eb ... that is not strictly the case. All lip trills , slurs and leaps are accomplished in part by using a tongue arch. If you have maxed out your tongue motion at Bb below high c how do you plan to continue going up? The tongue arch is like an elevator it should help you to compress and thereby speed up the air to achieve higher notes. Surely if you did practice out of the Irons book this was apparent. So you start out on the low c to second line g and lip slur back and forth. Both of these notes are below middle c yet a tongue arch is useful in speeding up the excerise. Likewise if you are playing a high g and want to slur up if you are already in the extreme eeee position where do you go?
My suggestion is to attempt to substitute a long aaaa when possible and save the extremes for a reserve.
Now for the full breath on every note or phrase. Have you ever had to play 1 note by itself to fill out a chord in a song? What about the 3 or 4 measure phrases? These do not require as much air as a full 8 measure phrase. At the end of a very short phrase an inexperienced brass player will feel a need to exhale before he or she can take a breath. If this overbreathing continues for any length of time the player will sometimes turn red or gasp for air. No you didn't run out of air for playing however, your body really likes to have oxygen in your lungs. What has hapened is you tooka full breath and used less than half. Now when you take a full breath you only replace half of the stale oxygen deprived air in your lungs. As this continues you end up gasping for air. Does this sound familiar?
Overbreathing really is a kind of self suffication (in the extreme). The exception was taken for high notes. Well here WE may be using different standards. Some people consider g on the staff to be high while others are referring to an octave or so over that. In this extreme upper register overbreathing becomes more apparent. Have you seen people get dizzy, lightheaded, or blackout. They were overbreathing. I know some people say if you release the pressure really slowly it will not happen. If you did not overbreathe and have so much leftover air under pressure it would not happen either.