For one plant, 4 20 watters could be 'alright' for one lowrdyer, but from what i see from other peoples grow journals, you would almost defiantly be looking at under an ounce. I am gonna order some lowryders tomorrow and am going to look to grow two under either a 250watt Envirolite or a 150/250 HPS. With CFLs you also have to take into account the color spectrum, although lowryder are auto-flower, they still have a veg period, its just very short and virtually unnoticeable, probably about a week and a half to two weeks. In regards to buying seeds, doctor chronic WILL ship to the US, just look for seeds there.
Peace out x