i think it might be nutrient problems especially seeing as i never use nutes for the first 2-3 weeks and i personally would say your light is ok it not too high because your plant is definately not stretching up wards and to be honest has started really well other than the yellow leaves, you will never clear them yellow leaves and bring them back to the nice green unfortunately, and they will probably drop off/dry first later in the growing. but yea as you say let the plant dry then flush it then do a ph test and that will tell you if the soil is too acidic or got too much alkalis, then as soon as you know you can do what you have to do to correct the ph problem if any.