There's too many factors to give an exact amount, however I do tend to drench the whole pot and let the roots find their way to the bottom on my first watering, allowing the plant to dry up and the roots will search down for the water over the next 5 days, though it may be different for you given that you aren't using a grow light. The water will dry at the top and 2 inches down within 3-4 days give or take 1-2 depending on many factors such as lighting, air circulation, temperature ect. Make sure you're pH is on point 5.5-6.5 when you water and good to check after adding fertilizer as well, some fertilizers will alter pH levels enough to cause harm, but you only need to check this once, Unless you change the serving per gallon, then I would check again to make sure that fertilizer doesn't impact it too much. After the first leaves appear, the plant needs fertilizer, Nitrogen - 4 Phosphorus - 3 K(Potassium) - 3 Is what I use, some like to use more and others use less. Try to keep it organic or as close as you can and for the love of god, please do not use Miracle Grow!
Good Luck and happy growing!