better try not to make them
fllushing should be never used as a means for anything other then a necessity. if ur plants r on the dry end & ready to water, well flushing does less harm then per sey, ur plants not ready for watering because u watered the day before & the soil is still very moist, & then that day ur flushed. This can then cause the plant to be overwatered which comes with its own unique set of problems; so u don't want that.
that should be fine as ferts goes, sometimes a little that seems insignificant goes a long way & remember u can always look to ur plants to tell u if they need more; easier to add more then try to remove overdosing by flushing.
prediction of male vs female might as well be a wives tale as far as generalizations go. I mean u could have a certain strain that tends to lean towards those tendencies for a male but there is just no way to tell. taller or shorter/stockier is much due to the light that is used in early veg, as much as the genes of a sativa vs an indica. my current grow that is about to finish for example is prominant sativa, of which I vegged 4 plants, & the 2 taller plants by a good 6-8 inches over the other 2 ended up being my females.
This is the worst part of growing but one plant, u give all the loving care for what is maybe 6 weeks to sometimes find out, all u get for it is balls, lol.