I would just use plain water until the sprouts reach about an inch tall. Then I would mix the
nutrient solution at about 1/4 strength until they get another couple of inches. Then I would mix it at about 1/2 to 2/3 strength tell the plants grow a bit more before mixing it full strength.
As for the numbers I wouldn't worry about that, for tomato's I would make sure the
nutrients were made for continuously fruiting plants. If you are still concerned about the numbers then just make sure the nutrients were specifically designed for tomato's, and by a reputable company.
P.S. Also make sure you are using hydroponic nutrients in a
hydroponic system.