3. It provides the best and by far the quickest way to develop the Head Register.
Some good players have developed a good tone over many years of practice and playing experience without Overtone practice (they actually can then produce Overtones quite easily), but this development takes much and much longer.

C.
1. Getting the "high squeak" (a hesitant version of Overtone 7 or 8). This puts your foot in the door of the Head Register.

2. Move down from the squeak to connect to Overtones 4, 3, 2 and 1.

3. Smooth out the transition from Head to Chest Register, and improve the quality of all Overtones.

4. Ultimately you have one combined Head-Chest Register. Each tone has its unique oral tract shape, and in that way there is a different register for every tone on the sax.

5. Never.
Overtone practice is the same as doing push ups or a daily run or walk. It keeps you in shape, and in fact keeps improving your tone forever.

D.
In which direction (forward, backward, up, down) should these body parts move to create an optimum open throat ?

1. the tongue is kept moderately forward
2. the soft palate goes up
3. the Uvula is pointed backward
4. the muscular pharynx wall is pulled back
5. the larynx ('Adam's apple) is kept down