Can't answer all your questions, can answer most though, if my answers are wrong, please correct me.

1)
Feminised seeds virtually guarantee female plants.
normally its 50/50 using these seeds its 99% chance of a female.
which is certainly a lot better
2)
Keeping a female in constant veg is pretty simple, just don't put it into flowering mode.
Basically keep it completely covered with light (24/0) or put it on an 18/6 timer. When you flower your plant's they go from 24/0 or 18/6 to 12/12.
Just don't go to 12/12, therefore your plant will never flower, and will constantly stay in veg form.
3)
I can't give advice on hydro growing, as I use soil. To keep a mother plant, I think your going to HAVE to have one plant in soil, otherwise you would have to create a second hydro unit, purely for your mother plant, because the light cycles will need to be different.
(When your flowering the rest, how could you keep one in constant light unless it was away from the main growing area?)
4)
A 400w Son-t lamp is, correct me if im wrong, a 400w HPS lamp
(I use the same bulb so am 90% sure). This will be fine for vegging+flowering, although I have heard using a Metal Halide bulb for vegging, and a HPS ( High pressure sodium) bulb for flowering has better results!

5) dunno bout hydro setups, so can't advise on nutes