Hey mate, 20/4 is fine for now and even when they sprout, i use 18/6 for veging but thats just personal preferance, what light a you using? If its a hps or mh then be careful not to have it too close otherwise you can fry the little seedlings when they sprout. As for watering... Its hard to say, depends on many things. In general when still that young i Water when the top of the soil looks dry, when there a bit older i wait for about top 2-3 inch feel really dry then water. Have a good read of the stickies on general forum and newbie forum, loads of Good info there! I am not sure if the above is the correct way its just how i do it btw, theres many differentnideas on whats best for growing. Good luck with the grow