lights are tough - lot of different situations - i'm a cfl grower so long tube fluoro's are a bit out of my 'normal'
but i think you will need at least 4 30w tubes, probably more, depends if you want to grow the plants 'natural' or with some training
training, such as LST or SCROG, can reduce lighting needs by letting you get the bulbs closer to the buds
if you let the plants grow without any training or topping, then you are going to need bulbs that cover the top and the sides - for good results you need a fluoro bulb within an inch or two of the plant buds
your plants will likely explode in height, 4 feet is the likely minimum, but depends a lot on strain