Yeast CO2 questions


I've just rigged up the CO2 yeast method following recipe posted by 
David Webb. I've connected it to an air-stone while building a reactor. 
Immediately noticeable effect are bubble streams coming out of cutted 
sections of stem plants and reduction in my pH. That must be a good 
sign. Now my questions:

1) Do I leave the CO2 bubbles coming out at full blast or reduce it with 
the air valve? 

2) Will reducing bubbles increase the preassure in the bottle and 
explode like that was posted in the last few mail.

3) Is it true that if I reduce the amount of yeast in my next mixture, 
would it last longer but with less bubble rate? Is there a catch to 

Thank you in advance.