veg for at least 3 weeks. minimum... for the health of the plant- not for size! Its not a clone (and I am assuming this is a bagseed first grow)...
I think you need another light... some people will tell you otherwise- but I think you do- and unless your poor theres no question... If you are poor, do you already have the MH's? if not this is my solution... Fuck MH's if your poor- (I have one and love it, but your situation could be different) Get a 3 pack of CFL's and put one one each plant an inch or 2 above it- and one between them- then rotate the plant somewhat often... (you can look at my journal and see a similar conception of this on the latest page) Then to flower I would suggest you get a 150 watt hps- you can get them for 69.99 from HTG on Ebay- if you call them you can often get hooked up and get cheaper shipping as well because then they dont have to pay ebay fees- there number is on ebay... The HPS has the right spectrum of light for flowering... an MH will work- but your yeild and buds wont be as high and hard- reportedly...
Now if you already have these MH's and two seperate ballasts? then... I would suggest getting some CFL's in conjunction with your MH- and use the 2700K red spectrum CFL's and I would recomend 6- cover the plants in them- 3 on each side- one on each plant- and one on each end and one in the middle- then rotate a little bit often... These CFL's have a better light spectrum for inducing flowering... there your cheapest solution at about 4-5bux a pop available at your local hardware store- there the currly fry bulbs- with a twist, and are the same size and connector as your typical household bulb- they are marketed at being environmental friendly- and they are cheap to run...
now for your final question...
two 70 watters shouldnt run it up at all- and either would the 150 hps i recommended... I have a 400 watt and have seen a very minisule increase- 10 bux maybe- max... and most report very little electrical stress- unless your running multiple 1000's or 600's...
Hope this answers all and more...
PM anytime if you need a direct answer quickly...
OB