Don't mean to rain on your parade. While it is not impossible to get 8 out of 8 females, the odds are really quite high. I just want you to keep an eye out. One hermie can ruin an entire grow.
I also do not understand how this statement can be true: "...I have been told that neither the plants nor the microbes can tell the difference between organic and chem ferts....". If the plants cannot tell the difference between chemical and organic ferts, why do organic grows not need to be pH'd and chemical ones do? Have you read or heard this from any other source than the guy at your hydro store? I am trying to learn about organics and everything I have read says that most microbes do not do well within chemical soils and with chemical nutes...I understood that it is not detrimental to the plant, it is just that the microbes cannot do their thing and it is therefore, while not detrimental, it is also not beneficial.