i would use about 5 mothers, you need to compinsate because obviously some wont make it, on 24/7 light regimen, unless using a 1000watt then i would throw it in 18/6, thats alot of concentrated light, when your mothers get big enough, Lst with it, to promote side branching, use this for your clones.
heres a pic to show what i mean.
this is still very small. it got alot bigger with alot more branches on it.
that will be fine, i would probably add fluoros to the mh or get a bigger mh, i probably wouldnt go under 3 mothers, or you can simply keep it from flowering and take as many as u possibly can.
5 mommies? I would go with more like 1 or two. You would have plenty of time to veg her out to supply that many clones. Thats a 2.5 to 3 ft mama.
I am always pruning my mothers to try to keep the size down.
As fo veg just use one light or the other bro. Its your preference how much light you need. You want he big HIDs for flower though.
I had the 250 mh growing 2 mother's in soil before and they were stretching to much,internode spacing was 8-10 inch'es.they grew up to 5ft in less than 2 month's.