Oh your hair is much longer than mine!
The longest layer of mine is finally just reaching my shoulder when unstretched and only 3cm below stretched.
Unfortunately, I can't really tell you how much product is appropriate for you to use. Have you seen the thread with techniques (Ice Queen Method, etc.)? Sometimes the results you want are more about technique than amount of product.
One of the reasons I fell in love with the AO Mandarin Magic Jelly is that it never made my hair crunchy.