Early variegation is not unusual. The first set of single and 3-fingered leaves often have blemishes and the plant will grow perfectly normal after that.
variegation is not a problem even if it continues. A little inconsistency in pigmentation... if it's part of some larger mutation or set of mutations, might be an issue, but only time will tell. It's rare. I've seen some with spotty leaves that just grew weird, but kept up with other plants... then buds formed like shit too. leaves weren't inconsistent 'green' but a bit oddly formed and not as perky. variegation alone was not the issue, in other words.
sure looks like you are watering mostly correctly given the context of a small plant in a too large pot. Keep watering a dimaeter around the small plant, but make sure that moisture goes all the way to the bottom. expand diameter as the plant grows. this trains a healthier, deeper root system and avoids superfical shitty root system. Don't choose the volume of water that makes you feel good... you give enough water to accomplish the task.. no less, no more. a little water coming out the bottom tells you that you accomplished the task.
In future, it's better to grow small plants in appropriately sized pots and pot up as necessary. Potting up is not stressful and contrary to popular belief about autoflwoers, does not shock them, lol. Total nonsense bro science
looks like penty of perlite per volume, so drainage and aeration is fine, too. Overwatering would be difficult to do. Saturating the substrate, or in this case a column of it around the too small plant, is not 'overwatering'. It's the correct thing to do. half-ass watering leads to problems, not the opposite. As long as you wait for top inch to dry (shallower in coco), you cannot overwater with a properly constituted substrate (enough drainage elements etc.. 50% in soil and 33% in coco is enough perlite or similar to make overwatering impossible for any rational behaviours and gives an optimal gas:water mixture in the substrate for optimal root health)